Rejuvenating Lead Acid Batteries

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Well-known member
Sep 30, 2020
Hi all. Over on the following thread:

I talk about the idea of rejuvenating Lithium Polymer (LiPo) batteries that we find in common electronics, although the thread itself is about Palm Pilot PDA's.

Here's some thoughts on rejuvenating Lead Acid batteries. I am specifically talking about Sealed Lead Acid (SLA) batteries of the type that power alarm systems, backup lighting systems, even trailer brakes, and motorcycles. I've been enticed to get into these experiments as I've bought SLA batteries several times which were new but didn't live up to their name plate rating. Batteries in stores sit around for way to long, maybe years. For some NOT fun, try explaining to someone at a battery store why the little cube battery you bought doesn't work even though their volt meter shows it's fine. These techniques can work with car batteries too, but are a little harder to implement. I'm not discussing anything about adding water to batteries but only maintenance free batteries. I did find some good information on YouTube, and lots of not so good information. So, you have to look at lots of info to know what's credible. You could search for rejuvenating lead acid batteries or desulfating lead acid batteries. I'll give anonymous credit to the helpful YouTuber's I found since I can't recall their channel names at the moment.

As I understand it, lead acid batteries hate sitting in a discharged state. Lead sulfate crystals form on the plates and increase the resistance. That means it's harder to charge and, when you discharge it, you get less energy out before the voltage drops too low. Many batteries are rated at the 20 hour discharge rate. Interestingly, you get less energy out of the battery if you draw the energy out faster. So, if it's a 5 AH battery (theoretically but not actually 5 A for 1 hour), then if you draw .25 A for 20 H, that's your 5 AH. The "C" rating is the same as the AH rating but without the hours. So, for the 5 AH battery, 1 C equals 5 A. You can generally charge these batteries at about .3 C. For the example battery, this would be 1.5 A. You can discharge at different rates but higher rates risk overheating the battery and, as stated, give lots less energy. I've found that discharging at the 5 hour rate, or .2 C gives about 85 % of the energy as doing so at the 20 hour rate or .05 C. Check battery label or specs for specifics.

You can charge one of these batteries with a standard constant voltage constant current lab power supply. This gives you more control over the process than with an automatic charger. If you're going to be closely watching the process, you can set the voltage to 14.7 V (in the case of my 5 AH trailer brake battery). If not watching so closely, set the voltage to 13.7 V (this is the float voltage shown on the battery). Then set the maximum current to .3 C, which is my case is 1.5 A. You connect the red positive lead of the power supply to the (usually red) positive terminal of the battery. You connect the black negative lead of the power supply to the (usually black) negative terminal of the battery.

If the battery is working normally, the current will immediately jump to the max of 1.5 A and the voltage on the power supply will reduce to whatever it takes to keep this current flowing. The voltage will gradually increase as the battery charges. Eventually the voltage will hit its limit of 13.7 V or 14.7 V. Then the current starts decreasing. I would consider terminating the charge when the current reaches 1% or .01 C, 50 mA in this case, or possibly .5 % or .005 C, or 25 mA in this case. Don't leave the battery at 14.7 V for a long time. Leaving (this particular) battery at 13.7 V should be safe. Do not charge the battery unattended until you've verified that it goes through a cycle with no problems. Monitor it for overheating. Do not leave it at 14.7 V.

To drain the battery, I use a microprocessor controlled electronic load tester East Tester ET5410 that I got from Amazon. This is a Chinese unit of pretty good quality. I think it was about $ 200. If you want to spend more, you can look at a Rigol product. If you want to spend way more, you could look at Tektronix or HP, etc.

It's not draining a lead acid battery that kills it as some believe, as long as you stay above 1.75 V / cell or 10.5 V for a 12 V battery. It's letting it sit in a drained state and having lead sulfate crystals form inside. To drain the battery, I set the load bank for constant current mode and set the current for the 5 hour drain rate of the battery or .2 C. For a 5 AH battery, this is 1 A. I set it to drain the battery down to 10.5 V. If it's working properly, I expect to see about 85 % of the name plate rating when I'm done. Remember, they're usually rated at a 20 hour rate. After running the drain at the 5 hour current, I'll run it at the 10 hour current (500 mA in this case) and then at the 20 hour drain current (250 mA in this case). Eventually, I'll get around to doing a charge cycle and a drain at the 20 hour rate to check for rated capacity. If the battery has its rated capacity, great. But, in my experience, they almost never do. A battery is generally considered at END OF LIFE it it's at 80 % of rated capacity.

But, you can often bring them back from the dead. Based on watching lots of YouTube videos, the consensus is that the magic desulfators generally don't work. There may be exceptions, but what you need is physics, and TIME. What may work, if the battery isn't internally damaged, is to simply charge it and drain it repeatedly. This may take 5, 10, or more cycles. As I said in the other thread linked above, batteries are weird and they have weird aging processes. Once you drain the battery and the load bank cuts off, the voltage on the plates rises again and you can run the load bank again for a while. So, I'll drain the battery at the 5 hour rate. A little while after the load bank shuts off, I'll start it again, and drain a little more energy out. Then, I'll do it again. Then, I set it to the 10 hour rate and do that a few times with the same battery. At this point, the battery is almost dead so it won't take 10 hours, maybe 1 hour, maybe a few minutes, etc. Then I set it to the 20 hour rate, and do that several times. Note that I'm not charging the battery, just restarting the load bank at lower and lower current levels. Once I consistently get almost no run time at the 20 hour rate, I get ready to charge the battery again. I note how much energy I got out of it on each of the main cycles.

Then I charge the battery again as noted above. I keep a note card with it and record each procedure. If I'm watching it, I charge it at 14.7 V. This pushes higher current into it (still limited by the constant current setting) for a longer time. This may help reverse the desulfation process. I do NOT leave the battery charging unattended at 14.7 V. If I'm going to leave, it's at 13.7 V. Again, note that the power supply will drop the voltage initially to maintain the constant current that was set. I do not leave the battery at all until I know it has successfully charged one cycle. If it starts getting hot or some cells start getting hot, I discontinue charging or reduce current. This is not a set it and forget it process.

I keep draining and charging the battery until I've reached 10 cycles or until it's performing at about 95 % or better of its rating. This is time consuming. Even though much of the process is automated, moving the battery from the power supply to the load bank and setting things takes some time. I've done this to several of these small SLA cube batteries. I've increased their capacity from 50 % to over 95 %. Once I've rejuvenated them, I put them on a "Battery Tender" 800 mA automated charging and maintenance device that maintains them at a float voltage. Note that I use the Battery Tender for maintenance, not charging.

You might say, why go to all this trouble? Just go get the battery replaced. Well, it's not so simple. As I said, the people at the battery store will pop a volt meter on it and say, it's showing 14.5 V or whatever. The battery is fine (even though it's not). They're resistant to do a warranty replacement. By the way, they also won't warrant them below about 10V. Also, it's likely that the replacement battery has been sitting on the shelf or in the warehouse just as long and will have the same problem. For some of these batteries, which I just use for experiments and maybe lighting when the power is out, they're not too critical. But, for my trailer brake battery (the 5 AH one), I darn sure want that thing to work if it's ever needed in an emergency. So, that's why I do this. Also, I just am curious to know how this stuff really works.

I'm also doing an experiment on one 2.9 AH SLA battery that I cannot recommend yet because I don't know the outcome, but you might find it interesting. As I said, once the load bank turns off, the battery voltage will increase. This battery has been very stubborn in completely discharging. I did the 5 hour drain current with a couple of restarts. Then the 10 hour drain current. Then the 20 hour drain current. Still the voltage kept rising at the end. That tells me it still has more potential energy, even if not much. I INTEND to flatten this battery to 10.5 V (not less). So, I've switched the load bank to constant resistance mode. I'm applying a continuous ~ 1000 ohm resistance to the battery down to 10.5 V. It's drawing about 10 mA. Every time the load bank shuts off, I turn it back on. I've been doing this all day intermittently. I'm hopeful that this process is reducing the sulfation internally. Once it really is flat, I'm going to charge it again. I will not leave it discharged.

I'd love to know if y'all have had experience working with batteries in this way.

May your bits be stable and your interfaces be fast. :cool: Ron
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Just checking voltage is useless, you need to also load test them, to see if they are capable of supplying current for 30 seconds, so I built a quick and dirty tester, using resistance tape from an old toaster, selected to have a 10A draw at 12V, and with a voltmeter to measure battery voltage. Meter is connected to the cables all the time, and a push button allows you to select in the resistor, so you see the resting voltage, and then press the button for 30 seconds, watching the voltage drop under load. Dying ones drop down rapidly to the cut off voltage of 10.6V, and really dead ones drop down immediately to almost nothing. Even works on lithium iron phosphate ones, though there you see good packs are pretty much flat, and drawing over 15A for a few seconds simply makes them shut off due to the overcurrent protection.
Stop Start lead acid batteries for cars, ie EFB & AGM technology, require special SMART chargers, not the older regular chargers. Buyer beware! Also LiPo batteries are not supposed to be drained past 80% of their capacity. I have many helicopter LiPos that have swollen up after charging by letting them drain too much.
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Hi all. I appreciate your comments thus far. Keep them coming. I want to acknowledge what @SeanBZA and @Mervyn Haynes have said and elaborate a bit. Maybe more than a bit. Batteries can be extremely dangerous. I'm VERY careful and meticulous, and I've made some bad mistakes. Batteries can contain huge amounts of energy. I was once tightening the screws on a 100 AH LiFePO4 battery with a crescent wrench. The wrench was just about the length of the distance between the terminals. The wrench was attached to one terminal and barely grazed the other for just a brief fraction of a second. There was a huge spark which scared the heck out of me and said, better than any actor cursing on any movie, what the heck are you doing dummy? Both the battery and the wrench now have a gouge where they touched. If the wrench had welded itself to the terminal, my house would have probably burned down. I immediately wrapped that wrench completely in packing tape except for the adjustable end. Ugly, but functional. Your watch, or your ring can do the same thing. Bridge a ring across the terminals of a battery and you'll probably get second or third degree burns and maybe lose a finger. I once connected one of these small SLA batteries to the load bank backwards. BAD idea. The load bank wasn't active, but it shorted the internal FET array and effectively shorted the battery. Note that I was expecting NOTHING and was unaware of any problem when I connected the wire. Within 1 second, the small jumper lead I was using, which was good for maybe 1 amp max, had melted it's insulation and was glowing red hot. I was within seconds of a life changing catastrophic event. I slapped the jumper lead away from the battery to get it disconnected as quick as possible. There was no time to "grab" or "disconnect" it. I burned a small stripe across my fingers as a reminder, and was literally only in contact with the (now bare) wire for 1/4 second.

I am not proud of these events. I'm glad that I and my house survived them. I don't just grab a soda, a comic book, and casually start connecting things. I'm very careful. There's an old adage in the construction industry - measure twice (or thrice) and cut once. This concept applies here although not the cutting part. Pre consider and pre plan EVERYTHING. RED positive wire goes to RED positive battery terminal. Other end of RED positive wire goes to RED positive power supply or load bank terminal. Same for the BLACK negative wire. If the terminals on any item are not color coded be doubly, triply careful. Are the settings on the load bank or power supply correct for your SPECIFIC battery and SPECIFIC battery chemistry. I wouldn't test multiple different chemistries at the same time. Is the voltage right, the current (compared to the battery rating), the voltage limit, the current limit? Triple check everything before connecting wires or activating equipment. This is not a spectator sport.

As @Mervyn Haynes points out, other battery chemistries are MORE dangerous than the relatively simple SLA (sealed lead acid) batteries I've mentioned here. Car batteries can explode or non sealed ones can leak acid. A shorted car battery can supply 800 A or more. That's WELDING current. For exotic car batteries, use automated chargers and maintainers so you don't destroy a $ 500 battery, etc. All lithium batteries are very snarky about upper and lower battery voltages. If you overcharge or over drain a LiFePO4 battery, you'll kill it. These are more resistant to fire internally but they can still provide plenty of current to start a fire externally for the bigger ones. Many of these have battery management systems (BMS) to prevent you from killing the battery. Hobby style batteries for model cars, boats, planes, helicopters, and drones are usually LiPo, not LiFePO4. They are usually built for high surge current, light weight, and usually no or minimal safety circuits. These are NOTORIOUS for catching fire or exploding if they're ticked off. YouTube for lithium battery fire. Note that, for the LiPo batteries mentioned in my Palm PDA in the other thread, I was discussing draining the battery in the device till the device shuts off. Nothing more. I was not manually draining that battery on a load bank.

So, I wasn't by any means trying to ignore the safety issues. If you're going to manually work with, test, charge, and discharge batteries: Learn the attributes of the chemistry and its limits. Learn the limits of your particular cell or pack. Plan exactly what you're going to do. Arrange everything carefully. Set everything carefully. Connect everything carefully. Activate everything carefully. Be conscientious and meticulous (that means slow and boring). Especially for LiPo, try to keep them away from flammables. One reason I stopped working with drones, other than FAA meddling, is that there is no place in my house that's not flammable. If a cell or pack ever starts swelling or overheating, discontinue immediately. If you can, get it into a flame proof bag or bucket of sand. If it explodes, flames can reach out several feet. LiPo battery fires are SELF FUELING and cannot be extinguished with water. If you can, figure out how to safely discharge it the rest of the way all the way to zero in a place where you don't care if it catches fire. Take it to a professional company like Batteries Plus and have it recycled. Note that it is illegal and dangerous to ship damaged batteries by USPS or a carrier like UPS or FedEx. A battery fire in a truck or plane could get people killed. It's not worth it just to make a warranty claim with a vendor. The vendor may not know that you can't do this.

That turned out to be a bit longer than I anticipated. But, this is critically important so I might as well get it out in the open. You may only get one chance to make a mistake. Stay safe. Other comments are welcome.

May your bits be stable and your interfaces be fast. :cool: Ron
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My rule of thumb for SLA batteries is that they typically only produce about 1/2 of their 'rated' AH capacity, before they hit that magic 10.5V limit. Any discharge past that voltage will likely permanently harm the battery. Also, they are HEAVY for their capacity. As a ham radio operator that likes to do "Parks on the Air" (POTA) activations, a SLA is just too heavy and has such a poor capacity rating that I tend to leave them at home these days, and use instead good brand name (BioEnno) LiFePO4 batteries. They also have a slightly higher terminal voltage, which works better with the 'nominal' 12VDC radios, which actually are usually much happier at 13.2VDC, especially when transmitting. And the LiFePO4's have a very flat discharge curve, even under load, which again makes my radios much happier when transmitting. I typically get 90-95% of the rated capacity out of my BIoEnno's, and they come with a dedicated smart charger, so I don't have to worry about having a bench full of test equipment to monitor them. LiFePO4's are also much more stable and safe than LiPO's. I have a variety of BiEnno LiFePO4's - 3AH, 6AH, and 12AH. I rarely use anything larger than the 6AH with a 10W PEP SSB (I run it 5W CW or digital modes) Elecraft KX2 transceiver, and it will run for hours on a 50% receive/transmit duty cycle.
@Dave New You make some good points. I just happened to be working with some SLA batteries so I decided to share this information. I'm not that fond of SLA's per se. For lots of small electronics and not so small backup power banks and boat motors and electronics, etc., the LiFePO4 is a really attractive option. I've got a couple of 100 AH Ampere Time (they recently changed their name to something else) LiFePO4 batteries ganged together in parallel with BIG cables for backup power. I can run a mini freezer, computer, and a lamp for a day or so. Longer power outages than that get really complicated. I've got a Victron Smart Shunt to monitor the parameters and power consumption. For those that don't know, a shunt is a very precise high current resistor element (looks like a metallic bar) placed in series with the main power source. It produces a very specific voltage proportional to current, which allows energy usage to be measured. As you said, I can get 100% of the rated energy out of the battery, which is really cool. LiFePO4 batteries usually have a BMS to keep one from over discharging, over charging, over current, shorting, charging while freezing, etc. You're right about weight of SLA, they are HEAVY for higher capacities. When someone uses the phrase heavy as lead, they mean it. The capacity thing is kind of a scam in the SLA industry. They say don't drain an SLA past 50 % to avoid shortening its life a lot. I don't believe if you drain an SLA flat to 10.5 V and immediately recharge it that it hurts it that much. But, I do believe that letting it sit in a discharged state even for a short time does hurt it. That's probably why they give the 50 % recommendation. So, if you stick to that logic, then yes, you only get half the energy out. Technically, though, I'm able to get 100 % of name plate rating from an SLA that's good and new or one I've successfully refurbished. Lead acid can be more desirable for engine starting with large current levels or in automotive applications where you don't have a custom LiFePO4 charger. But, LiFePO4 is definitely one of the best alternatives out there. LiFePO4 is much safer than LiPo in terms of fire danger.

May your bits be stable and your interfaces be fast. :cool: Ron
SLA will lose capacity with each cycle, and also with time, so pretty much will be dead after a few years, even if not actually having anything like a full discharge, and only having perhaps a 5% discharge before recharge. The ones used for old mining lamps are 2 cell packs, with a pouch surrounding each plate, and are wet, and those only have a 3 year life, before they are removed from service and either repacked or replaced. when new capacity is such they can do 48 hours of work illuminating the bulb, but are invariably pulled from service at 3 years, where they often are turned in for replacement, because they will not actually last a shift, even though the miner turns off the light for the 2 hour each way commute to the active face, and is working 8 hours at the face. Heavy duty plates, thick interconnects and well built, and they still do not last. The new lamps, with LED lamps replacing the incandescent ones, lasted 5 years before failing, and the miners welcomed the new lithium packs, half the volume and double the life, that have almost totally replaced the lead acid packs.

The mine packs are charged on a rack for 12 hours between shifts as well, about the best charge possible for SLA, but still drop off in capacity. Same for the electric batteries used for traction, though those do have a 6 month cycle through a battery shop, where they get the acid drained and filtered, the SG verified, and also get a full discharge and charge cycle per cell, used to get an exact capacity, to make the packs all from close matched cells. Charging on those is deliberately to the point of dissociation of water, with a fill system to make up, so they do not sulphate easily, and service will pull any weak ones out and replace them. Plus charged immediately at end of shift, so never left low. They still fail around 5 years and go for recycling, or are put into use for static power supply in larger banks.
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A most interesting post. Thank you.

Would you happen to know how an old sealed car battery and a small sealed battery (used in UPS and golf carts) would react to a permanently connected 13.5v (5A max) supply? I’ve done this for years as I need the battery as a backup for my electronic door lock should their be a power failure and to use the battery to power some 12v bulbs when the powers out.
Time passes so quickly doesn’t it, I‘ve just realised that these batteries are about 8 years on from the time they were taken out of service - so they are getting on a bit.
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@squirrel Thanks. I'm not a battery expert, just a person who's watched a number of videos, done lots of reading, and done a good bit of tinkering. So, I cannot give hard fast advice but I can share some general thoughts. Anything I say assumes the batteries in question are not fundamentally shorted or internally damaged. It assumes the electrolyte hasn't evaporated, etc.

My understanding is that SLA (sealed lead acid) batteries don't like sitting around in a discharged state. On the little 12 V 5 AH trailer brake battery I have, it says on the label - charge 14.5 V - 14.9 V and it reduces if it get's hot. And, float 13.6 V - 13.8 V and it reduces if it gets hot. It also says max charge 1.5 A, which is about .3 C. So, assuming this battery is pretty representative of this type of battery, that's where I chose my numbers of 13.7 V or 14.7 V. The lower one, the float voltage, should be safe for the battery over a long time. I have similarly had some of my little batteries attached to a power supply continuously. They're not critical for me, and it's more of a project and a vendetta against the ones that are under performing. In testing, I discovered that some of them had only about half the rated capacity. Hence, this thread. I cannot say if they never had their rated capacity, a distinct possibility, or if they degraded even though I had them on a power supply. I have been able to rejuvenate them to near rated capacity.

I can tell you that the Battery Tender device that I have keeps the batteries somewhere around 13.8 V in lead acid maintenance mode. So, I don't think there would be a problem leaving them on a power supply as you suggest. But, that doesn't necessarily guarantee that they can do what they're rated for. Based on my research, there doesn't seem to be any cheap easy way to test battery capacity. You can buy a battery tester from Amazon or the auto parts store for $ 30 - $ 50. These measure the internal resistance of the battery and the instantaneous cranking amps. But, they don't measure the actual amp hour capacity. As far as I know, the only way to measure amp hour capacity is to drain the battery while watching the output and tabulating what you're getting. My load bank does this automatically. You could do it manually if you were sufficiently motivated and willing to spend the time using a process called numerical integration. I can explain that if needed.

So, I think the only way to know what your batteries can actually do is to test them. 8 years is a bit old, but they might still work for your purpose. You could, if you wish, attach one of your 12 V lights to the battery and just time how long it runs. If you know the amperage requirement for the light, you could calculate how long the light should run. To maximize battery life, it's recommended not to pull more than 50 % of the energy out, although I'm doing more than that for testing. Don't run the battery below 10.5 V. Then, recharge it immediately. If you use the power supply for charging, set the current limit to about .3 C, IE the battery's AH rating x .3. If you cannot limit the current, depending on the size of the battery, the power supply may put in too much current. Something like a Battery Tender, or Battery Tender Jr. is a possible option for charging small batteries. My Battery Tender puts out .8 A. You can charge the battery until the current drops below .01 C (or 1 %) or even .005 C (or .5 %). For my 5 AH (same as 5000 mAH) battery, as an example, 1 % C = 50 mA and .5 % C = 25 mA. At that point, the battery is pretty fully charged.

If you have the motive and the patience, you can repeatedly charge and drain the batteries and see if your lights run longer. Do not leave discharged. (Side note, one YouTube video said if a battery is heavily sulfated, it might have to sit on a power supply at 14.7 V for a month or more before it starts accepting current. Theoretically, your batteries should be charged already.) You can continue this until you run out of patience and give up if the batteries are not working well enough, or you are satisfied with their performance. Remember that if you're pulling current out at faster than the 20 hour rate (.05 C), you may get less than rated capacity even if the battery is working. If you decommission them, consider recycling them at Batteries Plus or similar. If you replace them, you may wish to consider 12 V LiFePO4 replacements. These are much lighter, give 100 % of their rated capacity, and do not degrade as quickly. They must be charged with their own special dedicated chargers though. The charger current could be proportional to the C rating of the battery according to the recommended charge rate. They should have a BMS (battery management system) to protect the cells. They can be drained for testing similarly to SLA, but the cutoff voltages and drain currents are different. LiFePO4 batteries are not generally floated (maintenance voltage), so you have to top them off every couple of months. Having said that, my Battery Tender does have a Lithium maintenance mode that can keep these topped off, but I don't know exactly how it works.

That turned out to be longer than I thought, but I tried to include hopefully useful info. If you have more questions, feel free to ask. Maybe others with battery experience can jump in too.

May your bits be stable and your interfaces be fast. :cool: Ron
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If you haven't already, take a look at BatteryUniversity^com -lots of info on many type batteries.

I haven't played with small lead acid batteries much, but have kept a couple deep cycles 'ready to go' in case of power failure. Unless there is something I haven't heard lead acid should never be kept on a trickle charge, except maybe at low rates to try to desulfate for a limited time. Float voltage is critical for life, too high will 'boil' off the electrolyte, too low will reduce capacity and increase sulfate. Depending on the exact type battery the float voltage will vary, so following the manufacturer's ratings is a good idea. As mentioned try not discharging below 50% capacity.

I use a CBA (computerized battery analyzer) to check all my batteries, NMH, Pb, Li and I have come to trust it. WestMountainRadio^com sells them if you want to take a look. It is a bit expensive, about $200 last I looked, but especially for batteries in critical uses it is probably worth it. You set battery chemistry, capacity, and a discharge rate and it will plot a graph of the test results which you can later compare against other tests and see how the battery is aging. The software auto sets a safe cutoff voltage, but it can also be changed if needed. It can be set from 1 cell to multiples if testing a battery pack, and has a pass/ fail, usually at 80% rated capacity unless you change it. I like it, and have just found 5 NiMH AA cells that need to go to the recycle bin. Here's one type of graph from my 2 deep cycles which total about 100AH- if I attached it correctly!


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Depending on where the battery is kept it's temperature can be a big factor in it's useful capacity. Despite a number of drawbacks, NiCds held up good at low temps and did not mind being kept on a 0.1C or less continuous trickle charge. They also did not mind high current loads, they kind of liked the abuse to minimize 'memory. Back in their day I had a handful of wet cells but don't know how available they are now. At the time I thought of putting 11 or 12 in series as a car battery but the cost was quite high. I still have a copy of the General Electric Nickel Cadmium Engineering Handbook somewhere.

If you can find the battery manufacturer's date code decipher you can check how old a battery is before buying it. It's unlikely a supplier would bother doing periodic charges on small batteries so their age may be a useful. At work the batteries had dates and we would return them after a certain period of time, used or not. Another thought might be to keep a second battery in case the one in use gave out. With some more expense a solar battery charge regulator could keep a second battery charged whenever the engine is running and still isolate it against unintentional discharge. There are options depending on their cost vs need.
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I still have a copy of the General Electric Nickel Cadmium Engineering Handbook somewhere.
As do I. I got mine back in the early 80's when I was working at IBM Lexington, where we were pumping out a million typewriters a year. The new Models 50, 60, and 75 Selectrics had internal phrase memory that would go away on a power outage, so I was on a team that was designing a NiCd battery backup.
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I learned to type in high school way back in 1982. We had the old manual Remmington typewriters and you had to aggressively press each key about .5" to hit a key. We had one IBM Selectric in the room. I got to use it occasionally. That was the best feeling keyboard I've ever touched. The younglings have NO IDEA what they've missed. If you are reading this and you don't know what we're talking about, do a YouTube search on "typewriter". If you're reading this and don't know how to type, even as an adult, consider loading some typing tutor software on your laptop and learning. It takes lots of practice which is boring, but it's a really handy skill to have. :)

May your bits be stable and your interfaces be fast. :cool: Ron
Yes, I took typing in 7th grade in 1967 and like you, learned on manual 'mills'. I had also been taking piano lessons since I was six, and the typing teacher scolded me for 'bouncing my wrists' apparently due to my piano training. :) I will say that having touch typing under my belt did me all kinds of good when it came to typing up school papers on my dad's portable electric (which is now stored in my closet - haven't thought about it in decades, and it may not work any more from disuse). I started working with computers in high school using a ASR-33Teletype(tm) and a dial-up modem to dial in to the local college GE-255 time-sharing machine, which ran Dartmouth BASIC, ALGOL, and FORTRAN. I still have punched-paper tapes of the programs I wrote back then. I then got interested in ham radio, and got my Novice and Advanced tickets before going to college, where I majored in Electrical Engineering with a minor in Computer Science. That combination of computer skills and RF (plus knowing which end of a hot soldering to pick up) guided me through a long career of embedded systems programming for a variety of start-ups and finally as a Senior Technical Specialist in RF and Cybersecurity for a major automotive OEM.
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Although a number of co-workers would rather cut and paste than type, I don't mind the typing. Like many I started on the old mechanical ones. When I started working with computers, the old B3500s used Teletypes as their system console- I don't recall the model. I never took a course on typing, and although I do use 2 hands I am sure I am not doing it 'the right way'.

It's interesting to see some of the really old typewriters in some movies. One I can recall had a sticking key and the person typing (Harold Lloyd) poured some kerosene from the lantern into the typewriter to get it going. I don't know if people actually did that, but we did spray oil into a running Teletype when needed. When I was shown how to do it they thankfully told me to duck so oil from the spinning fan wouldn't get all over me.
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My sister used to work in a court, and stayed with a Selectric for many years as typing method, simply because the court computers, old 286 and 8080 XT and AT machines, with MSDOS 4.0, and Wordperfect, could not keep up with a typist capable of doing 30WPM plus consistently. She got annoyed with that 16 character buffer filling up and beeping after dropping characters, or whole words. The Selectric could keep up, and thus she stayed with it till the courts finally got 386 machines that were finally capable of keeping that buffer empty.

As she still types a lot, she uses now Win10, and Office 2008, and at least it can still handle the characters, even if the screen can occasionally take a second or two to show an entire line of input. Anybody looking at her keyboard though will find it hard to use, as all the centre keys, and the numeric pad, are all plain black ,with all the characters that were printed on them missing. Standard cheap Microsoft wired keyboard, she used to use older white MS keyboards, including one of the original split hump ergonomic ones, which she literally used to the point where the keys broke off the mounts, as the centre had worn away. next suffered the same fate, it probably had easily 10 billion keypresses over it's life. She worked a side job as well, as a transcriber for court documents, though she does not want to do that any more, the rate per page is low, and the audio from the courts can at best be described as poor on the best of them, often with whole pages of "inaud" for responses with only the general room mic getting anything, and for a lot of the rural courts also often having extraneous noise like roosters, crickets, frogs and goats as side tracks, along with dogs, cats and cows.
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all the centre keys, and the numeric pad, are all plain black
Stickers can be used to restore the missing labels. I've had to buy these on a few occasions. I'm typing this on my old Windows 7 laptop from 2010. I've had to go through a couple of rounds of stickers.

May your bits be stable and your interfaces be fast. :cool: Ron
I've never typed enough on a keyboard to wear out the markings. If I did it is quite possible I would be looking for a new keyboard since I don't think I could type without looking at the keys.
At least for the Selectrics, the key caps were double-shot injected molded (the white markings went all the way through the key cap, so you could never wear them off, but the electronic Models 50, 60, and 75, which had electronic keyboards used a 'Vacuform' like machine to 'inject' a dye 5 mm into the surface of the key caps. This was favored because you didn't have to keep a plant inventory of literally hundreds of different double-shot keycaps for all the 75-plus different regional keyboard layouts. Instead for the 'Vacuform' method, you printed the keyboard layout using dye in reverse on the rubber membrane, and then pulled it down over the blank keycaps on the keyboard assembly, heating it with an infrared lamp. The dye would then transfer into the keycaps. The only drawback was that you couldn't have white legends, since there is no such thing as white dye (duh!).

The same process was used for the IBM PC keyboards. They copied the design invented by IBM Lexington for their electronic typewriters. That's why the IBM PCs had beige keys with black legends, instead of black keys with white legends.

We spent a LOT of time testing various key and legend combinations, in a testing room with high-speed typewriter operators (30+ cps) and measured the number of mistakes per page of copy.

Also, the Selectrics and electronic typewriters were tested to 17.5M characters, which was considered 'life' for those machines. This was done using 'overhead robots' which was a box with solenoid plungers for each key position, driven by 8085 chips to exercise the typewriter. They used paper rolls similar to teletype paper rolls, and each roll was examined by hand for quality of print, etc.