Rapid discharge without use

Batteries and Chargers Rechargeable Batteries
1

I fully charged a number of NiMH batteries from 0mAh, some of which I thought I'd fully charged before and not used since. This was only few wks ago, and without use, they're all back at 0mAh again. They'd been stored next to each other in nylon bag in small pockets, so as to not be able to touch opposite ends. Bag was kept under stairs, where it had got quite warm (heatwave at moment). No direct heat.

Reason I'd looked for batteries was that PVR was reacting exceptionally slowly (or not at all) to remote. May be PVR problem, but thought I'd check batteries 1st.

Very grateful if you could help. Thank you.

Andrew.

2

What make are the batteries and are they LSD?

3

What method for measuring are you using to determine they’re at “0mAh”? What is their voltage?

PVR?

4

A PVR is a Personal Video Recorder, similar to a DVR or Digital Video Recorder like TiVo.

5

Yes, brand and size of battery, maybe source and price?
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Addendum* - What charger, how long did they charge, and what was the voltage at the end?
0v cells can have a very high probability of premature termination in a smart charger, with seemingly high voltage on (some) charger screens, and in reality get very little charge at all. I’ve seen a fair amount of that behavior.

FWIW, NiMh does not like being 0v. If you got them that way NEW, and you can return them I would. It indicates either a bad battery, really lousy storage, or both.
Even discharging a GOOD NiMh to 0v is hard on it.
If they are self discharging in a short time to 0v they are garbage. The heat should not matter much for a short period.

Absolutely DO NOT use the old recommendation of completely discharge, then charge. That was garbage info a decade ago for NiCad, and is even worse for NiMh. Discharge cycling should not go below 0.8-0.9v.

6

Info's incomplete because I'm not at all knowledgeable about batteries.

CORUN non-LSD, SIGShooter.

Reading on insertion, voltage on batteries 1·2V, BurningPlayd0h.

AAA, source/price not known, La Crosse BC-1000U, flydiver. I think charged ~5h. Don't know voltage at start/end - not observed as didn't mean anything to me (sorry, bit thick with this!) When I have looked, I think about 90% of voltage printed on them, but I'll check shortly. Apparent self-discharge has been instant - not a second or two, but instant.

I take it this, in manual, must be what you mean by old recommendation: "Old rechargeable batteries and those that have not been used for a long time need refreshing. This process will recover optimum capacity. Refresh mode will start with discharging the battery, then charging it. Repeated discharging & charging cycles will be launched, until no further increase in measured capacities is estimated, or 20 cycles, whichever comes first." Why was it thought to recover optimal capacity, if it doesn't? Unfortunately, this is what I've been doing since my initial post.

Thank you for your help.

Andrew.

7

Non-LSD batteries can rapidly discharge although going to 0 in a few weeks seems rather fast to me. But a quick search on Corun batteries seems to show that they are mostly used in devices that have a constant trickle charge (phones, emergency lights, etc) so perhaps such a rapid discharge is normal for them.

If it was me I’d fully charge them, see what voltage they are at immediately afterwards (should be around 1.45v or so and if not there’s something wrong with your charger or batteries), and then run a discharge test on half of them the next day and the other half the second or third day thereafter to see how rapidly they are discharging. You mentioned that self-discharge is instant; is that what your discharge test shows?

In my experience refreshing NiMh batteries is of use if they are LSD but not with non-LSD batteries because of their rapid self-discharge.

8

If you want to learn more about batteries, a good place to start is: https://batteryuniversity.com/
Bookmark it, and read the section you are interested in. If you know nothing, expect to have to read it a bunch, play around with the batteries and charger, and read some more. There’s a lot to learn and you won’t get it overnight. This forum is full of accomplished battery geeks.

The LaCross is a fine charger. I have a lower end unit I use a lot, especially for AAA since it has the 200mA as starting charge.
If you don’t understand the manual at this point you might watch some videos: La Crosse Technology BC1000 Alpha Power Battery Charger Review - YouTube
There are a lot out there.

I looked up the Corun website. They have a BUNCH of battery types.
I couldn’t find individual cells for sale, just small packs.

Nominal voltage for ALL NiMh is ~ 1.2v. A way to think about this is ‘middle working voltage’.
LSD should keep most of it’s capacity for a loooong time (many months). Non-LSD STILL should keep voltage for many weeks to a few months. If they lose voltage really quickly (days to a couple weeks), they are junk.

You can do a ‘refresh’, but with new cells that should not be necessary and takes a long time (days). Personally I’d do a ‘charge test’, which will charge>discharge to ~1.0v>recharge >> then tell you the discharge capacity. For AAA I’d use 200mA. For AA 500-700mA,

Once charged they should show about 1.4v+, BUT only for a day or 2. Then settle down to 1.3Xv and STAY there for a long time. If they don’t, then there is something wrong with them.

IMO, barring some actual defective hardware, I’d say the ‘software/you’ is still on a steep learning curve. You are doing something wrong, or not understanding what you are doing…yet. Hang in there, you’ll get it.

Note - have a REALLY smart buddy. Programmed software for a living. Excellent mechanic. Writes and sells programs for Android phones.
After a couple years of me working with him he’s only now starting to get the basics. Like a lot of people, I think the real problem is not really caring to put much effort into it.