Explain batteries to me like I’m Jesse Pinkman
March 14, 2025 2:44 PM Subscribe
Can rechargeable Ni-MH batteries cause actual damage to small electronics? How?
A couple years ago, I installed smart locks on my house with wireless keypads at the front and side doors. In the last 6 months, both keypads died after their single-use AAA batteries (once with Duracell, once with Energizer) leaked a few months into their lifespan. I filed a warranty claim for the latest one, and they’re sending a replacement keypad. In talking to their support technician, I mentioned my intent to exclusively use Panasonic’s eneloop rechargeable batteries going forward because those have never failed for me. The tech told me the keypad isn’t compatible with rechargeables, and that they can actually cause failures like I’ve experienced.
I know not to mix-and-match rechargeable and disposables — I’ve always used 2 of the same type and freshness together. I found this AskMe about why a device might say not to use rechargeables and many questions about how to best charge batteries, but no questions about this different-sets-of-batteries-affecting-each-other concern.
Is it possible (and likely/credible) that using rechargeable batteries in a device before switching back to disposables would affect the device in a way that causes those disposable batteries to fail and leak after a couple months? If so, why? If not, also why?
Note: I’m not directly looking for other theories about why the batteries might have failed, I mostly want to understand this theory that an Ni-MH battery can damage a device in a way that would cause future batteries to fail.
(For anyone who wants to offer a theory anyway: The keypads were both installed under covered porches where they were protected from both precipitation and direct sunlight. While it’s of course possible there’s some environmental factor involved, I don’t have any evidence to suggest one yet.)
A couple years ago, I installed smart locks on my house with wireless keypads at the front and side doors. In the last 6 months, both keypads died after their single-use AAA batteries (once with Duracell, once with Energizer) leaked a few months into their lifespan. I filed a warranty claim for the latest one, and they’re sending a replacement keypad. In talking to their support technician, I mentioned my intent to exclusively use Panasonic’s eneloop rechargeable batteries going forward because those have never failed for me. The tech told me the keypad isn’t compatible with rechargeables, and that they can actually cause failures like I’ve experienced.
I know not to mix-and-match rechargeable and disposables — I’ve always used 2 of the same type and freshness together. I found this AskMe about why a device might say not to use rechargeables and many questions about how to best charge batteries, but no questions about this different-sets-of-batteries-affecting-each-other concern.
Is it possible (and likely/credible) that using rechargeable batteries in a device before switching back to disposables would affect the device in a way that causes those disposable batteries to fail and leak after a couple months? If so, why? If not, also why?
Note: I’m not directly looking for other theories about why the batteries might have failed, I mostly want to understand this theory that an Ni-MH battery can damage a device in a way that would cause future batteries to fail.
(For anyone who wants to offer a theory anyway: The keypads were both installed under covered porches where they were protected from both precipitation and direct sunlight. While it’s of course possible there’s some environmental factor involved, I don’t have any evidence to suggest one yet.)
Best answer: Agree with soylent00FF00 that the slightly lower voltage of rechargeables is the typical problem they suffer. It is hard to imagine how low voltage is actually going to damage a device - whereas it is easy to imagine how high voltage is likely to. But companies tend to recommend against them because people put them in, the device malfunctions (sometimes in an infuriatingly occasional and random manner) due to the rechargeable batteries, and then they have to deal with returns, customer service requests, and people giving reviews and such saying that their product malfunctions, when in fact it functions exactly as designed, when operated according to directions.
(Having said that, I have personally used rechargeables in roughly one bazillion items where it says not to, and I generally find that if it works, it works. I just keep in mind that if it seems to malfunction maybe try an alkaline or whatever to see what happens.)
I tend to agree with your analysis that something like an eneloop seems to be manufactured to a higher standard because it is designed for repeated use over many years rather than single use & discard. I've got some eneloops sitting here that must be at least 10 years old, they're just fine. Any alkaline I had purchased at that time would be long gone.
The other reason people often recommend against using rechargeables for these kind of very low draw, very long term situations (clocks, for example - your locks are another) is that they are simply not the best match in terms of design, purpose, and economics. If you put a rechargeable in a clock (for example) you are taking a battery that costs 10X as much and locking it away for a full year (or whatever) with only one use. Rechargeables are meant to be used repeatedly, like 20 or 50 or 200 times in that year, and that is why they are worth spending more money on. Getting 5 uses out of them in 5 years just doesn't really "pay".
Maybe you're not really concerned about the economics of a couple of batteries, so irrelevant perhaps. But I've found it true that rechargeables don't last nearly as long as, say, a good-quality alkaline, in such applications. Rechargeables have a lower voltage to start with and then tend to self-discharge at hugely faster rates than alkalines. Like a nimh might self-discharge at a rate of 1% per day whereas an alkaline might self-discharge at 2-3% per year.
Yes, the self-discharge rates are on the order of 100X worse for rechargeables. They are designed to continually charge and discharge, not just basically sit there for a year.
Maybe you don't care about that either, but just a point to consider. You might have to change out rechargables every month or at the outside, two months, whereas alkalines or whatever might easily last a whole year or more.
Having said all that, I've used rechargeables in all sorts of those kinds of applications, and (given the caveats above, they definitely require more frequent changing) they seem to work OK as a rule.
posted by flug at 4:30 PM on March 14 [12 favorites]
(Having said that, I have personally used rechargeables in roughly one bazillion items where it says not to, and I generally find that if it works, it works. I just keep in mind that if it seems to malfunction maybe try an alkaline or whatever to see what happens.)
I tend to agree with your analysis that something like an eneloop seems to be manufactured to a higher standard because it is designed for repeated use over many years rather than single use & discard. I've got some eneloops sitting here that must be at least 10 years old, they're just fine. Any alkaline I had purchased at that time would be long gone.
The other reason people often recommend against using rechargeables for these kind of very low draw, very long term situations (clocks, for example - your locks are another) is that they are simply not the best match in terms of design, purpose, and economics. If you put a rechargeable in a clock (for example) you are taking a battery that costs 10X as much and locking it away for a full year (or whatever) with only one use. Rechargeables are meant to be used repeatedly, like 20 or 50 or 200 times in that year, and that is why they are worth spending more money on. Getting 5 uses out of them in 5 years just doesn't really "pay".
Maybe you're not really concerned about the economics of a couple of batteries, so irrelevant perhaps. But I've found it true that rechargeables don't last nearly as long as, say, a good-quality alkaline, in such applications. Rechargeables have a lower voltage to start with and then tend to self-discharge at hugely faster rates than alkalines. Like a nimh might self-discharge at a rate of 1% per day whereas an alkaline might self-discharge at 2-3% per year.
Yes, the self-discharge rates are on the order of 100X worse for rechargeables. They are designed to continually charge and discharge, not just basically sit there for a year.
Maybe you don't care about that either, but just a point to consider. You might have to change out rechargables every month or at the outside, two months, whereas alkalines or whatever might easily last a whole year or more.
Having said all that, I've used rechargeables in all sorts of those kinds of applications, and (given the caveats above, they definitely require more frequent changing) they seem to work OK as a rule.
posted by flug at 4:30 PM on March 14 [12 favorites]
I think the support rep and you are on different wavelengths. They aren't saying that rechargeable batteries cause leaks, they're saying the different discharge curve of NiMH compared to alkaline does not work well in their product.
posted by Rhomboid at 5:14 PM on March 14
posted by Rhomboid at 5:14 PM on March 14
What flug said.
Also - when an alkaline battery leaks (and they often do), usually you can typically just clean up the goopy / crusty mess, and everything is fine again. Usually the device after cleaning is just fine.
Waxing philosophical... if you have battery problems, and want to trade money for quality of life... the Energizer Lithium AA and AAA batteries are simply fantastic. They are single-use batteries but have many of the best qualities of Alkaline (higher voltage, shelf-life) and NiMH (not sagging under higher amperage draw) and I've never seen one of them go bad.'
posted by soylent00FF00 at 5:17 PM on March 14 [2 favorites]
Also - when an alkaline battery leaks (and they often do), usually you can typically just clean up the goopy / crusty mess, and everything is fine again. Usually the device after cleaning is just fine.
Waxing philosophical... if you have battery problems, and want to trade money for quality of life... the Energizer Lithium AA and AAA batteries are simply fantastic. They are single-use batteries but have many of the best qualities of Alkaline (higher voltage, shelf-life) and NiMH (not sagging under higher amperage draw) and I've never seen one of them go bad.'
posted by soylent00FF00 at 5:17 PM on March 14 [2 favorites]
Best answer: Is it possible (and likely/credible) that using rechargeable batteries in a device before switching back to disposables would affect the device in a way that causes those disposable batteries to fail and leak after a couple months?
No.
If not, also why?
Battery leakage happens when a battery's internal chemicals corrode its casing from the inside. It's brought on purely by the age of the battery, and is therefore more often seen in batteries housed inside equipment with a low current draw where the same battery stays in place for lengthy periods. The only way some previous occupant of a device's battery holder could possibly have any effect at all on this process is by having left behind a little pool of its own corrosive leakage. So as long as your rechargeables have been in good physical condition every time you've taken them out to get recharged, they'll have been doing your devices no damage.
Aside from their lower initial operating voltage compared to single-use alkalines, NiMH rechargeables are capable of delivering far higher currents when short-circuited. The only way I can see that difference resulting in damage to any device is if it has a pre-existing short-circuit fault that could draw enough current from the battery to cause intense internal heating. However, a short circuit bad enough to cause burnination when powered by NiMH cells would certainly drop the output voltage of an alkaline cell to well-below-totally-flat levels and stop the device working off those as well. I cannot think of any way that any such fault could be caused simply by fitting NiMH cells where alkalines used to be.
The way I'd interpret what the tech said to you is that their devices have known reliability issues with the generally lower operating voltages of rechargeable batteries (that's the "not compatible" part) and independently of that, rechargeables can also leak and cause that same kind of damage.
That said, I've got a crapload of NiMH batteries in regular circulation in my own household, most of which are not eneloops, and none of which are showing signs of leakage even though some are over ten years old.
posted by flabdablet at 6:17 PM on March 14 [6 favorites]
No.
If not, also why?
Battery leakage happens when a battery's internal chemicals corrode its casing from the inside. It's brought on purely by the age of the battery, and is therefore more often seen in batteries housed inside equipment with a low current draw where the same battery stays in place for lengthy periods. The only way some previous occupant of a device's battery holder could possibly have any effect at all on this process is by having left behind a little pool of its own corrosive leakage. So as long as your rechargeables have been in good physical condition every time you've taken them out to get recharged, they'll have been doing your devices no damage.
Aside from their lower initial operating voltage compared to single-use alkalines, NiMH rechargeables are capable of delivering far higher currents when short-circuited. The only way I can see that difference resulting in damage to any device is if it has a pre-existing short-circuit fault that could draw enough current from the battery to cause intense internal heating. However, a short circuit bad enough to cause burnination when powered by NiMH cells would certainly drop the output voltage of an alkaline cell to well-below-totally-flat levels and stop the device working off those as well. I cannot think of any way that any such fault could be caused simply by fitting NiMH cells where alkalines used to be.
The way I'd interpret what the tech said to you is that their devices have known reliability issues with the generally lower operating voltages of rechargeable batteries (that's the "not compatible" part) and independently of that, rechargeables can also leak and cause that same kind of damage.
That said, I've got a crapload of NiMH batteries in regular circulation in my own household, most of which are not eneloops, and none of which are showing signs of leakage even though some are over ten years old.
posted by flabdablet at 6:17 PM on March 14 [6 favorites]
what flabdablet said. NiMH batteries are far less likely to corrode than alkalines, which are filled with a corrosive chemical.
I bought my first Eneloops in 2016 and they and their Ikea-branded companions (I'm up to 30 now in regular rotation ) have never leaked.
posted by zippy at 8:04 PM on March 14
I bought my first Eneloops in 2016 and they and their Ikea-branded companions (I'm up to 30 now in regular rotation ) have never leaked.
posted by zippy at 8:04 PM on March 14
Response by poster: I think the support rep and you are on different wavelengths. They aren't saying that rechargeable batteries cause leaks, they're saying the different discharge curve of NiMH compared to alkaline does not work well in their product.
This is what the support tech wrote: "I'm so sorry to inform you that our team would recommend against using rechargeable batteries as they are not compatible with our products and can cause damage to the internals. This may have been the direct cause of the corrosion and if these batteries are currently being used for the second Keypad, they may put it at risk for the same outcome."
Yes, the NiMHs have some real downsides for this application (they drain so very fast), so it's completely fair that they discourage their customers from using them. But it was the alkaline Energizers that corroded away the contacts, and blaming the eneloops (especially after immediately shipping me a replacement based on just the photograph I initially sent them, then asking for serial numbers later) feels off.
I try to swap out the eneloops regularly, and that works pretty well for me. Since 50% of the alkalines I've used in these keypads have leaked and destroyed the keypads, I'm honestly not interested in gambling another $80 unit on longer-lasting batteries. It seems likely that I've had wildly bad luck (or Level had one horrible production run in 2023) and it won't happen again, but I feel like I'd be asking for trouble at this point. And it feels wasteful not to make good, repeat use of these eneloops AAAs that I don't need for anything else.
I'm still curious whether anyone can come up with any crazy sequence of events that would back up this rechargeable -> alkaline -> ooze narrative because I really want this company to not be blaming me for what seems like bad hardware. It's weird for new-ish alkaline batteries to leak so quickly ... twice ... in two of the same device ... when they were different brands of alkalines ... and I guess I'm just reaching for a myth that explains it all.
posted by katieinshoes at 8:32 PM on March 14 [2 favorites]
This is what the support tech wrote: "I'm so sorry to inform you that our team would recommend against using rechargeable batteries as they are not compatible with our products and can cause damage to the internals. This may have been the direct cause of the corrosion and if these batteries are currently being used for the second Keypad, they may put it at risk for the same outcome."
Yes, the NiMHs have some real downsides for this application (they drain so very fast), so it's completely fair that they discourage their customers from using them. But it was the alkaline Energizers that corroded away the contacts, and blaming the eneloops (especially after immediately shipping me a replacement based on just the photograph I initially sent them, then asking for serial numbers later) feels off.
I try to swap out the eneloops regularly, and that works pretty well for me. Since 50% of the alkalines I've used in these keypads have leaked and destroyed the keypads, I'm honestly not interested in gambling another $80 unit on longer-lasting batteries. It seems likely that I've had wildly bad luck (or Level had one horrible production run in 2023) and it won't happen again, but I feel like I'd be asking for trouble at this point. And it feels wasteful not to make good, repeat use of these eneloops AAAs that I don't need for anything else.
I'm still curious whether anyone can come up with any crazy sequence of events that would back up this rechargeable -> alkaline -> ooze narrative because I really want this company to not be blaming me for what seems like bad hardware. It's weird for new-ish alkaline batteries to leak so quickly ... twice ... in two of the same device ... when they were different brands of alkalines ... and I guess I'm just reaching for a myth that explains it all.
posted by katieinshoes at 8:32 PM on March 14 [2 favorites]
I'm still curious whether anyone can come up with any crazy sequence of events that would back up this rechargeable -> alkaline -> ooze narrative because I really want this company to not be blaming me for what seems like bad hardware.
I think you're thinking about this harder than they are! I think they're sending out a broad Don't Use Rechargeables In Our Thing Ok without sweating the details, and if some guy told the support tech that maybe it caused your problem, the tech isn't getting paid to game it all out, whatever.
The double bank shot of some batteries turning the device into evil!device that makes other batteries turn bad is just... a lot.
posted by away for regrooving at 12:17 AM on March 15 [2 favorites]
I think you're thinking about this harder than they are! I think they're sending out a broad Don't Use Rechargeables In Our Thing Ok without sweating the details, and if some guy told the support tech that maybe it caused your problem, the tech isn't getting paid to game it all out, whatever.
The double bank shot of some batteries turning the device into evil!device that makes other batteries turn bad is just... a lot.
posted by away for regrooving at 12:17 AM on March 15 [2 favorites]
...where, to be perfectly clear, "a lot" means "complete, utter, total, irredeemable horseshit".
Seriously, I think any electronics engineer would struggle to design a device that does this on purpose, let alone accidentally.
posted by flabdablet at 2:49 AM on March 15 [2 favorites]
Seriously, I think any electronics engineer would struggle to design a device that does this on purpose, let alone accidentally.
posted by flabdablet at 2:49 AM on March 15 [2 favorites]
Maybe you're not really concerned about the economics of a couple of batteries, so irrelevant perhaps. But I've found it true that rechargeables don't last nearly as long as, say, a good-quality alkaline, in such applications. Rechargeables have a lower voltage to start with and then tend to self-discharge at hugely faster rates than alkalines. Like a nimh might self-discharge at a rate of 1% per day whereas an alkaline might self-discharge at 2-3% per year.
The main problem I encounter with rechargeables versus alkalines is that rechargeables (eneloops as well as conventional NiMH) tend to deal badly with low temps. The chip-reading cat flaps just need alkalines to keep working for a few months instead of less than a month during winter (occasional low temps of -5⁰C, average just above freezing just inside of where those cat flaps are mounted). Apart from that eneloops are fine, and keep charge in anything I put them in for close to a year if they're not, or rarely, used.
So using rechargeables in locks may be disadvised if they have to deal with freezing temps. Otherwise there's no reason not to if the devices don't complain about the lower voltage.
posted by Stoneshop at 3:45 AM on March 15 [1 favorite]
The main problem I encounter with rechargeables versus alkalines is that rechargeables (eneloops as well as conventional NiMH) tend to deal badly with low temps. The chip-reading cat flaps just need alkalines to keep working for a few months instead of less than a month during winter (occasional low temps of -5⁰C, average just above freezing just inside of where those cat flaps are mounted). Apart from that eneloops are fine, and keep charge in anything I put them in for close to a year if they're not, or rarely, used.
So using rechargeables in locks may be disadvised if they have to deal with freezing temps. Otherwise there's no reason not to if the devices don't complain about the lower voltage.
posted by Stoneshop at 3:45 AM on March 15 [1 favorite]
I do think, having read your last update with the direct quote, that they’re fibbing to you. This particular type of non-malicious not-really-truth-telling happens a lot across the different levels of an organisation’s customer service. People sort of extrapolate in a CYA way from a low level of knowledge.
posted by lokta at 3:52 AM on March 15 [4 favorites]
posted by lokta at 3:52 AM on March 15 [4 favorites]
An old computer programmer's joke:
Q: What's the difference between a computer salesman and a used car salesman?
A: The used car salesman knows when he's lying to you.
Now that everything has a computer in it, that joke is quite a lot less funny.
posted by flabdablet at 3:56 AM on March 15 [5 favorites]
Q: What's the difference between a computer salesman and a used car salesman?
A: The used car salesman knows when he's lying to you.
Now that everything has a computer in it, that joke is quite a lot less funny.
posted by flabdablet at 3:56 AM on March 15 [5 favorites]
Yes, the NiMHs have some real downsides for this application (they drain so very fast),
Actually drained, or just 'gotten below low-batt voltage', which, as noted, occurs sooner in devices designed for use with alkalines? Do you have a charger that shows the charge state when they're inserted?
Because if they're really drained, I'm quite sure alkalines will get drained in about the same time as they have similar capacities , and this will be fairly rough on AAA cells, and pretty much raises the chance of leakage.
posted by Stoneshop at 4:07 AM on March 15
Actually drained, or just 'gotten below low-batt voltage', which, as noted, occurs sooner in devices designed for use with alkalines? Do you have a charger that shows the charge state when they're inserted?
Because if they're really drained, I'm quite sure alkalines will get drained in about the same time as they have similar capacities , and this will be fairly rough on AAA cells, and pretty much raises the chance of leakage.
posted by Stoneshop at 4:07 AM on March 15
flabdablet: Now that everything has a computer in it, that joke is quite a lot less funny.
Basically, both the computer salesman and the car salesman are feeding you AI bullshit these days (so by extension are just computer output devices), and only experts can see the AI crap being total horse puckey.
posted by Stoneshop at 4:11 AM on March 15
Basically, both the computer salesman and the car salesman are feeding you AI bullshit these days (so by extension are just computer output devices), and only experts can see the AI crap being total horse puckey.
posted by Stoneshop at 4:11 AM on March 15
if they're really drained, I'm quite sure alkalines will get drained in about the same time as they have similar capacities
NiMH self-discharge rates can be, as noted above, as much as a hundred times that of alkalines. Panasonic claims that its Eneloop cells are virtuous outliers in that regard, though my own tests give me no particular reason to believe them; there seems to be a lot of variation in self-discharge rates within every brand I own. So these days I just mark my AA and AAA cells with a H if I've seen them go flat in less than a month in the TV remote, and use those in high-current, frequent-recharge applications like toys and head torches instead.
posted by flabdablet at 4:32 AM on March 15 [1 favorite]
NiMH self-discharge rates can be, as noted above, as much as a hundred times that of alkalines. Panasonic claims that its Eneloop cells are virtuous outliers in that regard, though my own tests give me no particular reason to believe them; there seems to be a lot of variation in self-discharge rates within every brand I own. So these days I just mark my AA and AAA cells with a H if I've seen them go flat in less than a month in the TV remote, and use those in high-current, frequent-recharge applications like toys and head torches instead.
posted by flabdablet at 4:32 AM on March 15 [1 favorite]
Household batteries have leaked and caused damage to many a device in my home, so there's that.
posted by theora55 at 9:12 AM on March 15
posted by theora55 at 9:12 AM on March 15
I think the new class of disposable lithium batteries that soylent00FF00 referred to is the best option here. While they cost more they are better in every better in everyday to the alkaline batteries.
Project Farm recently tested a bunch of AA batteries and concluded that Powerbowl and Bonai came out on top for price, but if it were my locks I would spend the extra cash and get the Energizers.
posted by zenon at 11:38 AM on March 15
Project Farm recently tested a bunch of AA batteries and concluded that Powerbowl and Bonai came out on top for price, but if it were my locks I would spend the extra cash and get the Energizers.
posted by zenon at 11:38 AM on March 15
Battery companies can be surprisingly generous in compensation if their products damage electronics. Mrs Coke Spoon's insulin pump got damaged by a battery, and when she contacted the brand about it they offered to cover the replacement cost of the pump (in the end the pump manufacturer replaced it, and the battery company mailed out a bunch of free batteries).
posted by Jessica Savitch's Coke Spoon at 11:45 AM on March 15 [1 favorite]
posted by Jessica Savitch's Coke Spoon at 11:45 AM on March 15 [1 favorite]
> can cause damage to the internals. This may have been the direct cause of the corrosion and if these batteries are currently being used for the second Keypad, they may put it at risk for the same outcome.
I think this part of their comment is just plain incorrect.
However, they may have something in their approved scripts for dealing with product issues that says something like, "using batteries different from those specified may lead to product damage." That is a true statement in the generic sense, though not in the case of your specific batteries.
So, they are just completely uninformed/wrong, or something like this.
Either way, I don't think it is anything to worry about too much.
posted by flug at 6:49 PM on March 15
I think this part of their comment is just plain incorrect.
However, they may have something in their approved scripts for dealing with product issues that says something like, "using batteries different from those specified may lead to product damage." That is a true statement in the generic sense, though not in the case of your specific batteries.
So, they are just completely uninformed/wrong, or something like this.
Either way, I don't think it is anything to worry about too much.
posted by flug at 6:49 PM on March 15
Thank you for posting this question. The answers were interesting and useful. Now, who the fuck is Jesse Pinkman and did you really need me to look that up in order to learn more about batteries?
posted by JimN2TAW at 9:19 AM on March 23
posted by JimN2TAW at 9:19 AM on March 23
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The main issue with NiMH rechargeable batteries is that they have a slightly lower voltage (~1.2V) than Alkaline batteries (~1.5V). Some devices are fine with that, some not. A common problem is the device may work fine, but give spurious "low battery" warnings.
I can't think of any plausible way in which using NiMHs for a while, then switching to Alkalines, could cause the latter batteries to fail. That sounds... not likely. Occam's razor here is the tech support person was lying or misinformed.
posted by soylent00FF00 at 3:32 PM on March 14 [7 favorites]