Topping off almost full Eneloop batteries

[Owen Lucas]

I have a flashlight with 4 AA Eneloop Pro (NiMH 2550 mAh) that sits in my car for emergencies. Haven't used it in a few months but want to make sure the batteries are topped off. Is it OK to charge NiMH batteries when they are mostly charged or should they be drained first for best efficiency / capacity?

 

[y_p_w]

It's fine. I use Eneloops (and some of the other LSD NiMH batteries made by Sanyo or Fujitsu) on a daily basis in all sorts of devices including flashlights, air pumps (using AA to D adapters), computer mice, remotes, etc. I rotate them in and out without worry about how much or how little I used them before recharging. I do have pairs and quads that are kept together, but mostly I top off the singles. I'll use them in a mouse for anything up to a day to a few months, or in a single-cell flashlight for just a day. The cycle longevity assumes full cycles, and partial cycles theoretically are OK. I certainly haven't noticed anything like catastrophic failures, and I've had some of these batteries in regular use for nearly 8 years. I rarely drain them fully, and when I do it's from not paying attention. I'll sometimes just charge up batteries that haven't been used after the last charge just to top them off.

I have had some fail, but that tends to be somewhat random. A couple ended up leaking, but only with some whitish stuff coming out of the positive terminal and not damaging anything like I've seen with alkalines. I had some alkalines that got stuck in a Mini-Maglite. Some were in cordless phone that was constantly being charged and discharged over 7 years without being rotated. That was to be expected with that kind of use with any batteries.

And Eneloops are incredible. I found some first generation Eneloops with a 2007 date code on them. I had put them away in a carrying case for mayne 9-10 years, and when I tried them they still could power some electronics. So I jus put them back in my rotation. I also have some Sony CycleEnergy branded ones that I bought years ago (a 2008 date code) and they mostly get used in (appropriately enough) a Sony radio. But those were definitely made by Sanyo.

 

[Rand]

yes nimh you should keep them charged.. and use a smart charger to not overcharge.

They do self-discharge between 1%-10% per month depending on the actual battery construction.

 

[y_p_w]

yes nimh you should keep them charged.. and use a smart charger to not overcharge.

They do self-discharge between 1%-10% per month depending on the actual battery construction.

The OP did mention (nominal) 2550 mAh Eneloops. Granted I believe the 1900 mAh versions are a better choice for any number of reasons, including overall longevity, lower internal resistance, and lower self-discharge. Also - long term testing seems to indicate the the 1900 mAh versions (even the oldest ones) can typically have more capacity retention than previously rated. The rating is supposed 85% after a year and 70% after five years, but I've heard it's closer to 70% after 10 years. I mentioned the batteries that still had useful charge after 9-10 years.

And of course the conditions (temp and humidity) will make a difference. Cooler is of course better for reducing self-discharge.

 

[y_p_w]

I have a flashlight with 4 AA Eneloop Pro (NiMH 2550 mAh) that sits in my car for emergencies. Haven't used it in a few months but want to make sure the batteries are topped off. Is it OK to charge NiMH batteries when they are mostly charged or should they be drained first for best efficiency / capacity?

I'd think that for your purposes, the 1900 mAh versions might actually be better since their self-discharge characteristics are better. My preference is to have a lot of them and to rotate them in and out of different devices. I suppose the big issue in a car will be heat, although in the trunk is typically cooler than in the passenger compartment. However, I have no issue topping them off after sitting around for a while. I understand that they actually lose a big chunk due to self-discharge in a few days, which then settles down.

 

[Owen Lucas]

I'd think that for your purposes, the 1900 mAh versions might actually be better since their self-discharge characteristics are better. My preference is to have a lot of them and to rotate them in and out of different devices. I suppose the big issue in a car will be heat, although in the trunk is typically cooler than in the passenger compartment. However, I have no issue topping them off after sitting around for a while. I understand that they actually lose a big chunk due to self-discharge in a few days, which then settles down.

Good points and thank you for the informative replies. The flashlight endures subzero temps in the winter and up to 100* temps in the summer. I chose the pros because I figured higher mAh would be better for a 1150 lumen flashlight, which I think 4AA is probably underpowered but that's all that can fit in it's compact design.

I never knew about the different self discharge characteristics of the pro vs regular. I see why it is a better idea since the flashlight is for emergencies, so having a functioning one with slower discharge batteries is better than higher current batteries that discharge earlier. I seems the pros are more for immediate higher power use like a camera or if I were to use the flashlight daily.

 

[Owen Lucas]

yes nimh you should keep them charged.. and use a smart charger to not overcharge.

They do self-discharge between 1%-10% per month depending on the actual battery construction.

Smart charger all they way and off into the Battery Daddy they go.

 

[y_p_w]

Good points and thank you for the informative replies. The flashlight endures subzero temps in the winter and up to 100* temps in the summer. I chose the pros because I figured higher mAh would be better for a 1150 lumen flashlight, which I think 4AA is probably underpowered but that's all that can fit in it's compact design.

I never knew about the different self discharge characteristics of the pro vs regular. I see why it is a better idea since the flashlight is for emergencies, so having a functioning one with slower discharge batteries is better than higher current batteries that discharge earlier. I seems the pros are more for immediate higher power use like a camera or if I were to use the flashlight daily.

I like to rotate the batteries for single AA, dual AA, quad AA, single AAA, dual AAA, etc. Don't have any 3 AA devices that I regularly use any more, and those are a pain. I don't know if there's necessarily even wear, but I'm thinking they never get to the point where they reach the equivalent max cycles. And some of my devices are rarely used, but the batteries will randomly go in and out. Never had anything ever wear out unless if was charged in the device in a cradle, and those are notorious for killing batteries. Topped off all the time. I just like having them. I'd previously used a Maha charger instead of the Sanyo chargers that charged in pairs, but I mostly use a couple of Panasonic BQ-CC17 chargers. They're slow but I've never had any batteries that were too hot to touch while charging.

I think the longevity standard that Panasonic/Sanyo uses is 60% of nominal max charge. Certainly for your purposes as an emergency light, you're not likely to ever reach that point, unless there's just a random failure. And you might even want to stash some spares with it.

I rather like the 1900 mAh Ikea LADDA now. I don't know why they claim only 1000 cycles, but for the most part I don't think it matters. I'm thinking they could be the same quality as other batteries from the FDK factory.

LADDA rechargeable battery, HR06 AA 1.2V, 1900mAh - IKEA

LADDA rechargeable battery, HR06 AA 1.2V, 1900mAh You reduce costs and waste by switching to rechargeable batteries, especially if you are a frequent user of traditional alkaline ones. In addition, you will always have working batteries when needed! The battery is ready to use.

www.ikea.com

 

[Owen Lucas]

I like to rotate the batteries for single AA, dual AA, quad AA, single AAA, dual AAA, etc. Don't have any 3 AA devices that I regularly use any more, and those are a pain. I don't know if there's necessarily even wear, but I'm thinking they never get to the point where they reach the equivalent max cycles. And some of my devices are rarely used, but the batteries will randomly go in and out. Never had anything ever wear out unless if was charged in the device in a cradle, and those are notorious for killing batteries. Topped off all the time. I just like having them. I'd previously used a Maha charger instead of the Sanyo chargers that charged in pairs, but I mostly use a couple of Panasonic BQ-CC17 chargers. They're slow but I've never had any batteries that were too hot to touch while charging.

I think the longevity standard that Panasonic/Sanyo uses is 60% of nominal max charge. Certainly for your purposes as an emergency light, you're not likely to ever reach that point, unless there's just a random failure. And you might even want to stash some spares with it.

I rather like the 1900 mAh Ikea LADDA now. I don't know why they claim only 1000 cycles, but for the most part I don't think it matters. I'm thinking they could be the same quality as other batteries from the FDK factory.

LADDA rechargeable battery, HR06 AA 1.2V, 1900mAh - IKEA

LADDA rechargeable battery, HR06 AA 1.2V, 1900mAh You reduce costs and waste by switching to rechargeable batteries, especially if you are a frequent user of traditional alkaline ones. In addition, you will always have working batteries when needed! The battery is ready to use.

www.ikea.com

$6.99 is a great price for what could be re-wrapped Eneloops. You must be pretty well organized to rotate batteries, I will have to give that a try.

 

[AP9]

Some smart chargers also have the capability to "test-discharge" the batteries at a specified current to estimate their remaining capacity. If there's an extended stretch (many months) where the batteries aren't actually used or deeply discharged, it might be a good idea to use that to "refresh" them. Other than that, the occasional "top-off" charge should will be sufficient -- with a smart charger, of course.

 

[y_p_w]

$6.99 is a great price for what could be re-wrapped Eneloops. You must be pretty well organized to rotate batteries, I will have to give that a try.

Not organized at all. I mark most of the set with a Sharpie or without markings but where I recognize the date code. The singles just go into a case and I randomly rotate them in and out. I figure it all evens out. I've never logged my usage, and I've never run any batteries through a testing cycle. I figure it's not worth burning through cycles just to figure out how much capacity there is left. Besides - I rarely use batteries all the way through until they stop working. With LSD NiMH it's a lot easier to just use them and then recharge. I might use a flashlight for about 10 minutes where a full charge might last 15 hours. Or a wireless mouse for a week when on a full charge it should last at least 12 months. At least considering new capacity. I've even heard that partial discharges are considerably better for cumulative NiMH battery life than complete discharges.

I've ended up buying so many different ones over the years, and that helped a bit to know which ones are which - especially with different date codes. My favorites were the Costco packs where the AAs were two shades of blue, and the AAAs were two shades of green - at least until maybe 2015 when Costco started selling white Eneloops. It was kind of bizarre though since sometimes they had special packs with 10 AAs - so it was 5 of each shade of blue. They usually had 4 AAAs, but split into both shades of green. To get a color matched set of 4 I combined them from two sets. I used them in flashlights and one remote that used 4 AAAs. Found a photo of one assortment. I think I bought two of these back in 2014.

I don't know if it's really worth it for the price, but it's easier to sort sets when there are so many different brands with different labels. You know - it can be pretty obvious that they're sets of 4 if they look different and I only have 4. The other way I did it was just put a dot on the label with a Sharpie. I didn't like like using labels because they would typically come off.

 

[y_p_w]

Some smart chargers also have the capability to "test-discharge" the batteries at a specified current to estimate their remaining capacity. If there's an extended stretch (many months) where the batteries aren't actually used or deeply discharged, it might be a good idea to use that to "refresh" them. Other than that, the occasional "top-off" charge should will be sufficient -- with a smart charger, of course.

There's a bit of controversy over whether or not "conditioning" is a good thing or not. I know with older generation NiMH hybrid car batteries, the general idea was to use them only for partial discharges and charges in the middle of the charge range - around 40-75%, or what they called the "sweet spot" which is supposed to keep it out of the range where most of the degradation occurs. It was easy to do since the battery was only supplemental to help with acceleration and to soak up energy from regenerative braking. Some hybrids are still on the same NiMH batteries after two decades.

 

[Owen Lucas]

Not organized at all. I mark most of the set with a Sharpie or without markings but where I recognize the date code. The singles just go into a case and I randomly rotate them in and out. I figure it all evens out. I've never logged my usage, and I've never run any batteries through a testing cycle. I figure it's not worth burning through cycles just to figure out how much capacity there is left. Besides - I rarely use batteries all the way through until they stop working. With LSD NiMH it's a lot easier to just use them and then recharge. I might use a flashlight for about 10 minutes where a full charge might last 15 hours. Or a wireless mouse for a week when on a full charge it should last at least 12 months. At least considering new capacity. I've even heard that partial discharges are considerably better for cumulative NiMH battery life than complete discharges.

I've ended up buying so many different ones over the years, and that helped a bit to know which ones are which - especially with different date codes. My favorites were the Costco packs where the AAs were two shades of blue, and the AAAs were two shades of green - at least until maybe 2015 when Costco started selling white Eneloops. It was kind of bizarre though since sometimes they had special packs with 10 AAs - so it was 5 of each shade of blue. They usually had 4 AAAs, but split into both shades of green. To get a color matched set of 4 I combined them from two sets. I used them in flashlights and one remote that used 4 AAAs. Found a photo of one assortment. I think I bought two of these back in 2014.

I don't know if it's really worth it for the price, but it's easier to sort sets when there are so many different brands with different labels. You know - it can be pretty obvious that they're sets of 4 if they look different and I only have 4. The other way I did it was just put a dot on the label with a Sharpie. I didn't like like using labels because they would typically come off.

I like the Sharpie method, I'll try to incorporate it into my storage system, Battery Daddy. A decent as seen on TV product, it even made it into Costco for a while!

 

[y_p_w]

I like the Sharpie method, I'll try to incorporate it into my storage system, Battery Daddy. A decent as seen on TV product, it even made it into Costco for a while!
View attachment 106834

Once I put off buying a special deal at Costco that had about everything, including a carrying case. Amazon seems to be selling this directly, although I'm not sure where it comes from (old stock from Costco?). It could be new, but it reminds me of the set that was at Costco 6-7 years ago.

 

[y_p_w]

yes nimh you should keep them charged.. and use a smart charger to not overcharge.

They do self-discharge between 1%-10% per month depending on the actual battery construction.

I'm not even sure where anyone can find a timed charger any more. I wouldn't recommend a "smart charger" that charges in pairs since pairs can be unbalanced. I remember someone at work who got an Eneloop kit at Costco that came with one of the old Sanyo branded chargers that only charged in pairs. He said he was going to use the batteries in his single-cell Logitech mouse. I certainly wouldn't recommend using those since they can over/undercharge pairs being charged together.

Now the low self-discharge Ikea LADDA batteries that are clearly made in the FDK factory in Japan are kind of odd. Ikea sells a variety of smart chargers, but their batteries are labeled with a standard timed charge. This is for the 2450 version, but the 1900 version I have says "190 mA for 16 hours".

I've opened up my Panasonic chargers. The back says only for charging Panasonic NiMH batteries, but I don't really think there's anything specific about their batteries that would mean similar batteries couldn't be charged. However, I saw that the charging IC in it was from some Taiwanese company (Elan Microelectronics), and when I looked it up it was a generic charging circuit for NiMH or NiCad batteries. Nothing fancy and it didn't come from one of the big companies like Texas Instruments or Maxim Integrated. But it's been reliable for over 8 years and seems to do the job quite. I looked up the company now, and they don't seem to be in this market any more.

 

[JHZR2]

Keeping NiMH below 100% SOC doesn’t matter a lot. It’s not like a lead acid battery…

Keep them in a narrow state of charge, topping up every so often. Not a huge need to top them up and get them warm too often. But they do self discharge. Eneloops not so bad as the more traditional and more energy dense versions.

 

[y_p_w]

Keeping NiMH below 100% SOC doesn’t matter a lot. It’s not like a lead acid battery…

Keep them in a narrow state of charge, topping up every so often. Not a huge need to top them up and get them warm too often. But they do self discharge. Eneloops not so bad as the more traditional and more energy dense versions.

It might actually be good for certain applications since the center of the charge range is supposed the "healthiest" for NiMH. The way hybrid car batteries work is that they're supplemental and serve as an energy sink for the energy recovered from regenerative braking, but the engine charges the batteries when convenient. However, that allows the batteries to be used within a limited range (often 40-75%) where they don't typically get stressed out.

The thing about Eneloops, the newer FDKs, and all the low self-discharge batteries made in the same factory is that they are ridiculously reliable. I've had the older-style Sanyo batteries go bad. They were easy to spot because they had "HR" stamped on the negative terminal. I actually sorted a lot of these by brand/rated capacity/etc. knowing they were identical for the most part. I had (mostly 2500 mAh) versions with the Energizer, Duracell, Maha PowerEx, Maxell, and even Sanyo brand names. But they has issues with failing, although I never had one with a serious leak. However, I remember in the early days there were some odd ones, like Energizer 1200 mAh rated AAs that were labeled as made in the US.

 

[y_p_w]

I like the Sharpie method, I'll try to incorporate it into my storage system, Battery Daddy. A decent as seen on TV product, it even made it into Costco for a while!
View attachment 106834

I just got one of these:

Storacell Battery Management Home Page

Storacell

storacell.net

I'm not sure I'm using them the correct way. I've been inserting them the opposite way where the positive terminal just fits perfectly into a hole. I like them because it's easy to just insert one in any random slot and it doesn't take up a whole lot of space.

 

[y_p_w]

Just thinking of this as I just got a new pack with the current version of the Panasonic BQ-CC17 charger and 4 BK-3MCCA batteries. Both have 2022 manufacturing date codes for June or July. The batteries are stamped in a different style but otherwise look identical to the white Eneloops that I bought with 2014 date codes. They haven't changed anything about those, including the model number and the specs. I do also have the newest Ikea LADDA 1900 which I suspect come off the same line, although I can't account for the 1000 cycle rating as opposed to 2100 for the BK-3MCCA.

The charger is different even though it's got the same model number. The back of my older one has the date code (YY-MM) heat stamped into the plastic. The newer one is printed in some sort of ink and a YYMMDD exact date. The older charger has "AA" in a box while the newer one has "AE". I haven't opened it up, but I did years ago for the older one and saw it had a charging circuit from Elan Microelectronics, which is no longer in that business. The newer one also has really bright green charging indicators, although they're still buried behind the plastic and it's still hard to tell which battery it represents until both are lit. The older one has a duller (not sure if it's just worn) green color and less brightness. Panasonic obviously found a different charging circuit supplier, although I'm thinking these are probably just commodity parts at this point.

 

[y_p_w]

Just thinking of this as I just got a new pack with the current version of the Panasonic BQ-CC17 charger and 4 BK-3MCCA batteries. Both have 2022 manufacturing date codes for June or July. The batteries are stamped in a different style but otherwise look identical to the white Eneloops that I bought with 2014 date codes. They haven't changed anything about those, including the model number and the specs.

There is a slight difference in the batteries other than just minor label printing differences. Of course the date code is different, but I'd expect that after 8+ years. But mine newest ones have a message that they're "Not intended for sale outside North America" and I assume the French language equivalent message. Found a photo.