How low to run my NiMH AA's?

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wahoowad's picture
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How low to run my NiMH AA's?

I have a low drain electronic device I use frequently that uses 6xAA and I like to use my rechargeable NiMHs. The device has a customizable ‘low battery’ alarm I can set between 6.2 to 8.3 Volts. What is a good setting for using NiMHs? I wasn’t sure how low I can run them??? Flat Stare

All my AA NiMHs are rated at 1.2v but charge to around 1.45v. Is the rated 1.2v still considered a full charge? If so, should I expect to run my cells down to…1.1? (setting would be 6.6v)??? Down to 1.05v? (setting would be 6.3v)????

johnnydoe's picture
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From what I know, 0.9V is considered empty for a nimh.
Since 6.2 is the lowest you can go you should go for that.

StyXSIS's picture
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Nimh shouldn’t go below 0.9v really, if you go past that, you run the risk of making those cells that go below 0.9v hi resistance cells as they will heat up when charging and not fully charge with the amps it should get but voltage alone. It’s that voltage that makes them heat up and useless in the end as your charger will receive feedback of a fully charged battery before it’s charged with the amps it needs. You can fix them, but that will need multiple high voltage drains and low amps charges of each cell on it’s own to get them back to maybe if your lucky 90 percent. So to make sure your batts stay good that torch has alredy given you a good voltage of 6.2 as a stoping point as it should be 5.4 volts if it’s 6 cells, but 6.3 is good also.


Last seen: 1 hour 9 min ago
Joined: 06/19/2013 - 19:16
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Location: Seattle, WA

1.2v is ‘nominal’ voltage (sort of operating middle).
Full/warm is 1.45v. They won’t hold there long generally dropping to 1.35v within 24 hours even without use.
They’ll hold @ 1.2’ish for a long time.
At 1.0 you should consider them empty, especially when using in a series as one of them will be a weak link.
If you push a PACK too far the weak link goes dead > the device pulls voltage through the dead cell and it may reverse the polarity, effectively killing that cell.
If it’s a soldered pack > you’ve killed the pack.
I’d use 6.2v minimum, maybe even up to 6.5-6.6. Probably won’t be a lot of effective operating difference.

Take a look at AA NIMH discharge curves.

To Air is Human, to Respire….Divine.

snakebite's picture
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a higher cutoff is safer and wont impact runtime enough to notice.try 7.0.
that should be near the “knee” in the discharge curve.
i have a few items that should have this feature.
fortunatly i dont leave the rig on recieving till it dies and the pack falls on its face during transmit when it is discharged.
i just transmit and the display goes out.

Kodachrome40's picture
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When voltage under load ( or very shortly after ) reaches around 1.20-1.25v then I recharge eneloops. With 1500-1800 charge cycles available, I don’t hesitate to charge them up.