Backyard Aquaponics
A place to discuss aquaponics

If I have a device with 12 AA NiMH rechargeable batteries with 11 of them showing 1.34v and one showing 1.28, is that enough difference to cause a problem?

It's a cordless vacuum cleaner that keeps shutting off.

Is that before or after charging?

After an overnight charge.

What are the voltages after it cuts out?

it cuts out when fully charged as soon as you turn it on. I figured perhaps it required a minimum voltage to operate, and perhaps if one battery was bad it might be a drain on the rest or something.

I have second unit that someone gave me with the same problem that I was thinking of using as a UPS. It's 12v, and it has a built in charge controller with battery temperature reader.





* Oops! They have 10 AA batteries, not 12

Yea, the one bad cell might be going into reverse voltage and the device might have a low voltage disconnect... NiMH cells aren't too expensive to replace though. Have you tried one of the higher voltage batteries from the 2nd unit in the first one?
I wouldn't waste any time trying to make a UPS from it, unless you put a full set of new cells in, but using a Lead-acid battery may be less expensive for more capacity.

Coles is selling a 4 pack of AA 2200 mAh NiMH batteries for $7 at the moment, so I thought now might be a good time.

I figured I'd just get a 12v air pump and run it as a backup.

When they say "dont mix battery types", do they mean dont mix chemistry types, or dont put a new coles (2200 mAh NiMH) battery in place of the faulty one (1300 mAh NiMH)?

And thanks for the help so far

Types generally means mixing NiMH with Lithium or NiCd for example, but it is also a good idea not to mix new with old batteries, as it will shorten the life of the new battery. Mixing different capacities in series is also a bad idea, you should replace the lot together.

Cool.

Thanks.