Care for Ni-MH batteries

[paulri]

I just received an 8 pack of rechargeable AAA ni-mh batteries; I only needed 4 but the 8 pack was only $1.50 more. There was an information sheet (if you want to call it that) that came with the batteries but my question was not addressed there.

The first ones appeared to have a low charge after unwrapping them; I put them in a flashlight and could barely see anything. I charged them up and there was plenty of light. The second set of four has not been used/charged up.

My question: What is the best way to extend the life of the four that I don't need right now, as long as possible--charge them up now and store them, or just keep them in storage for a year or two until I need them, and then charge them up? Or should I mix them up with the other four, charging them all up and using them all? I think it would be easier for me to keep these four separate, until the others go bad, but I'd rather do what is best to extend their life as much as possible.

 

[PandaBear]

Keep them between 20-80% charge and don't keep them somewhere hot. They will also have a calendar expiration date in addition to cycle life. I'd rotate them around just to make sure they aren't forgotten and the charge drops too low.

 

[bobdoo]

NiMH are not lithium ion, and are not cadmium.

Charge them to 100%, they will very slowly discharge, and may still be at 90% after a year. They DO NOT have 'memory', and you do not need to charge/discharge them multiple times to 'fix' them. They will develop a bit more capacity after the first couple charges, but not a huge %.

LiIon have the longest useful life by charging 20% to 80%. This is not true of NiMH.

I have sets that are probably 20 years old, now. They still work fine, but at somewhat reduced capacity.

I used to buy exclusively Eneloop, but now buy amazon's stuff. There isn't enough difference to matter.

 

[92saturnsl2]

I disagree with the above poster [Pandabear]. Ni-Mh are not sensitive to being charged fully. In fact, they self-discharge, so 100% charge is the goal when storing them (provided you have a smart charger that isn't on a timer or doesn't overcharge.) They will deplete slowly, so if placed in indefinite storage, charge them every few months, or every year if they're LSD (low self discharge) type.

I've gotten 5-10+ years easily out of a set of Ni-Mh batteries-- the off-brands (like EBL, Westinghouse, Camelion, etc.) have lasted longer than the well known brands (Energizer, Duracell, Philips, Kodak, etc.) in my experience. If you can find genuine Eneloops, you can't beat them, but they're pricey.

Li-Ion batteries are a whole different animal-- fully empty or fully charged degrades the battery when kept there. The ideal storage condition is 60-70% charge.

 

[y_p_w]

What's your goal in all this?

For me, the gold standard for consumer NiMH batteries are the low self-discharge ones now made by FDK Fujitsu and that originated with Sanyo as the Eneloop. I'm not sure why, but they're sold as "ready to use" but are supposedly charged to about 70% at the factory. I think that's with potential long-term storage in mind. However, they also discharge really slowly.

However, I doubt it's really that important once you've got them. You're not going to have the kind of fine-tuned control over the state of charge that you might be able to get with a computer battery. Inevitably you're going to charge them until the charge terminates.

I have heard of older NiMH batteries used in first generation hybrid cars. Those were designed such that the charge range would be kept within 40-75%. Some called it the "sweet spot" where it didn't stress out the battery and it was expected that it could allow batteries to last a long time if they were only kept in that range for supplemental power and to recapture energy from regenerative braking, as well as possibly charge up from the ICE. Those have lasted a long time but they tended to be expensive to replace.

However, I'm judging this by the FDK Fujitsu/Sanyo designs, which I've rarely seen fail. I had sets that eventually failed in a cordless phone, but cradle charging tends to do that. I have had traditional NiMH batteries fail, where the wouldn't charge. A smart charger would flash some sort of error condition. However, those were rated at maybe 500 full charge-discharge cycles (which I doubt I met). I think they were probably failing early, but that happens.

 

[paulri]

These are amazon basics rechargeables. The AA Am Basics that we have, have lasted a long time, so I figured I'd go with them.

NiMH are not lithium ion, and are not cadmium.

Charge them to 100%, they will very slowly discharge, and may still be at 90% after a year. They DO NOT have 'memory', and you do not need to charge/discharge them multiple times to 'fix' them. They will develop a bit more capacity after the first couple charges, but not a huge %.

LiIon have the longest useful life by charging 20% to 80%. This is not true of NiMH.

I have sets that are probably 20 years old, now. They still work fine, but at somewhat reduced capacity.

I used to buy exclusively Eneloop, but now buy amazon's stuff. There isn't enough difference to matter.

 

[ripcord]

The most important thing is to not let them get hot. Charging them up every 6 months if not being used is good, too.

 

[y_p_w]

These are amazon basics rechargeables. The AA Am Basics that we have, have lasted a long time, so I figured I'd go with them.

They have a variety of different suppliers. There were some indications that some were made by FDK Fujitsu based on their low self-discharge design, but they would be labelled as being made in Japan.

NiMH are known to do better if kept in the middle of the charge range, but almost nobody uses them that way. It would take a huge amount of discipline to achieve that given the equipment most people use them and the equipment used to charge them that has some sort of termination condition and not something like a phone battery with onboard diagnostics. But I don't think they're quite like lithium-ion batteries that are actually damaged (and might not recover) from being discharged below a certain level.

I've bought AAA Ikea LADDA. Last time I got them on sale for less than $5 for a 4-pack. I don't really use the AAAs that much, but I have one pack that I haven't opened yet. But it's clearly low self-discharge so I'm not so worried about it. I just couldn't resist at the price. I've got existing flashlights that use 4 AAAs but I already had two sets of 4th gen (Panasonic) Eneloops for that and those are basically just for emergency use where the LSD batteries are nice to have. But whatever AAAs I have usually go in pairs - like for a remote control or a wireless keyboard. But the thing I really like is to just keep a reserve pair charged and then swap that in every month or so, although I don't keep any records.

 

[92saturnsl2]

NiMH are known to do better if kept in the middle of the charge range, but almost nobody uses them that way. It would take a huge amount of discipline to achieve that given the equipment most people use them and the equipment used to charge them that has some sort of termination condition and not something like a phone battery with onboard diagnostics. But I don't think they're quite like lithium-ion batteries that are actually damaged (and might not recover) from being discharged below a certain level.

Ni-MH is not nearly as sensitive as Li-Ion when it comes to discharge / charge / storage / maintenance, as long as you don't overcharge them. They do require a smart charger that uses -dV termination (where the charger senses a voltage dip at the end of charge) for optimum life.

Li-Ion batteries can be charged by any dumb charger that cuts the charge off at 4.2V (typical Li-Ion chemistries). You can buy them for a few bucks. Good chargers will taper current as the battery approaches 4.2V to get to full capacity. Nothing magical about charging Li-Ion batteries. Phone batteries on-board diagnostics like you mention is simply a microprocessor reading impedance and software in the phone telling you how much the battery has degraded.

 

[y_p_w]

Ni-MH is not nearly as sensitive as Li-Ion when it comes to discharge / charge / storage / maintenance, as long as you don't overcharge them. They do require a smart charger that uses -dV termination (where the charger senses a voltage dip at the end of charge) for optimum life.

Li-Ion batteries can be charged by any dumb charger that cuts the charge off at 4.2V (typical Li-Ion chemistries). You can buy them for a few bucks. Good chargers will taper current as the battery approaches 4.2V to get to full capacity. Nothing magical about charging Li-Ion batteries. Phone batteries on-board diagnostics like you mention is simply a microprocessor reading impedance and software in the phone telling you how much the battery has degraded.

There’s a lot more. Certainly the ability to do Coulomb counting and keep track of how many cumulative cycles, as well as store an estimated capacity.

 

[y_p_w]

Keep them between 20-80% charge and don't keep them somewhere hot. They will also have a calendar expiration date in addition to cycle life. I'd rotate them around just to make sure they aren't forgotten and the charge drops too low.

Old topic I know, but I've never seen NiMH batteries that had any kind of expiration date. I remember finding a set of 1st gen Sanyo Eneloops in a pocket and I'm thinking there were there for at least 8 years. They worked in a flashlight just fine and I just charged them and put them in a rotation.

At least with Sanyo/FDK the batteries all have some sort of manufacturing date stamp. I have some that are pretty old. Many have scratches or where the label is cut, but they're still doing fine after 15 years.

I can't say the same for older style NiMH batteries. I've had those fail after a few years - even the high quality ones made by Sanyo.

 

[92saturnsl2]

Old topic I know, but I've never seen NiMH batteries that had any kind of expiration date. I remember finding a set of 1st gen Sanyo Eneloops in a pocket and I'm thinking there were there for at least 8 years. They worked in a flashlight just fine and I just charged them and put them in a rotation.

At least with Sanyo/FDK the batteries all have some sort of manufacturing date stamp. I have some that are pretty old. Many have scratches or where the label is cut, but they're still doing fine after 15 years.

I can't say the same for older style NiMH batteries. I've had those fail after a few years - even the high quality ones made by Sanyo.

I just did some cleaning of the basement recently and discovered some Ni-Cd and NiMH cells that I stowed away and forgot about.

The Ni-Cd were "D" cells rated at 5000mAH, the NiMH were "C" size rated the same. I know exactly when I bought them (2012) and they were still in sealed wrappers holding 4 each, never been used. Both were Tenergy brand, one I've had decent luck with in the past.

Put them on a SkyRC battery analyzer, and the Ni-Cd cells read about 4200mAH capacity, the NiMH "C" cells were a little less, in the 4000mAH ballpark. I don't recall these two batteries measuring much higher than that when new. For grins I tested them both on a 2A discharge, and they did fine.

So I gather if there's an expiration date for these Nickel based rechargeable batteries it's quite a while. That said, I haven't done any kind of cycle testing of them after being in storage so long.

 

[y_p_w]

I just did some cleaning of the basement recently and discovered some Ni-Cd and NiMH cells that I stowed away and forgot about.

The Ni-Cd were "D" cells rated at 5000mAH, the NiMH were "C" size rated the same. I know exactly when I bought them (2012) and they were still in sealed wrappers holding 4 each, never been used. Both were Tenergy brand, one I've had decent luck with in the past.

Put them on a SkyRC battery analyzer, and the Ni-Cd cells read about 4200mAH capacity, the NiMH "C" cells were a little less, in the 4000mAH ballpark. I don't recall these two batteries measuring much higher than that when new. For grins I tested them both on a 2A discharge, and they did fine.

So I gather if there's an expiration date for these Nickel based rechargeable batteries it's quite a while. That said, I haven't done any kind of cycle testing of them after being in storage so long.

I'd think the biggest worry would be contact corrosion if the storage conditions are wet.

 

[bunnspecial]

Honestly, the best thing you can do with any nickel-based battery chemistry is use it. They should be charged to 100%, and not allowed to go flat. The latter is especially important in multi-cell packs since they may not all discharge at the same rate and you can end up reverse charging one when you do go to charge it, and reverse charging is a sure path to quick death. The latter can even happen in devices with removeable batteries if they left and allowed to self discharge, as the one that goes flat first can end up getting reverse-charged by the remaining ones. Also, even when charging separately, many common chargers will actually charge two batteries in series, so the whole reverse charge thing can happen if you throw a completely dead one in. The general guideline I have been told/follow is that they should not be allowed to go below 1V/cell, but I have also recovered/used ones that were well below this when I first used them(you can get this desparate when you have a battery pack that's no longer in production and also really difficult to recell).

ALL Nickel based batteries are susceptible to memory effects, contrary to the above. Most people think NiMH don't and Ni-Cd does, but it can happen with both chemistry types. NiMH is probably a little less susceptible, but Ni-Cd also isn't as bad as many will have you think. Many chargers for both battery types have a "refresh" cycle that does a controlled deep discharge, and I've seen guidelines that recommend this being used every ~10 charge cycles.

One of the other things I'll mention is that if you want the longest service life, you should invest in a good quality charger. NiMH is not very tolerant of overcharging. When they are charged at constant current, full charge can be detected by a small voltage "dip" but it's quite subtle. I've charged them on bench PSUs a few times(not the best idea necessarily with NiMH, but can be done) and if I'm charging say a 2000mAh cell at 200mA(normal rule of thumb I use for most battery chemistries for "gentle" charging is a charging current equal to 1/10 the capacity in Ah) the voltage might hit 1.42V briefly-as in for a couple of minutes-and then drop to 1.40V. If you're doing this on a bench PSU and not actively monitoring, this can be easy to miss. A NiCd, on the other hand, might hit 1.45V, stay there for an hour, then drop to 1.35V.

The best way to charge NiMH is actually by monitoring temperature change. I've rebuilt several multi-cell NiMH packs that incorporate a thermal diode to do exactly this. I'm not sure if any stand-alone individual cell chargers can do it.

Along those same lines, and someone else mentioned this, heat kills NiMH. This is true in charging also, and part of why temperature monitoring is a good thing. NiMH cells really don't like to be above 40ºC or so. That's not a temperature you're likely to have in storage(a little over 100ºF), but is an easy one to hit in rapid charge and discharge.

Summary, though:
1. Charge them fully, but don't overcharge on a quality charger
2. Let them run down reasonably, but not flat
3. Don't let them sit flat
4. Keep them cool