How can I tell the charge on a battery?

[ab1ht]

Hi all,

Looking at the typical charge vs. time graphs on many batteries (especially CR123s), there is a pretty flat line followed by a sharp drop off. Examples on this thread: https://www.candlepowerforums.com/threads/67078

Is there a test that I can perform whereby I put a battery under a brief load and know the number of amp-hours remaining (given the manufacturer's data sheet, of course)?

Thanks.

 

[shadowjk]

It's generally about as accurate as "full" or "not full".. ;-)

 

[fishinfool]

Hi all,

Looking at the typical charge vs. time graphs on many batteries (especially CR123s), there is a pretty flat line followed by a sharp drop off. Examples on this thread: https://www.candlepowerforums.com/threads/67078

Is there a test that I can perform whereby I put a battery under a brief load and know the number of amp-hours remaining (given the manufacturer's data sheet, of course)?

Thanks.

I use a ZTS MBT-1 to check on all of my batteries (nimh, li-ion, primaries) but it only gives you a percentage of the available capacity and NOT the number of amp-hours remaining.

 

[digitor]

Is there a test that I can perform whereby I put a battery under a brief load and know the number of amp-hours remaining

Short answer: No.

Long answer: Maybe you can get a pretty close approximation if you perform an accurate test on a cell that you have plenty of previous test data on. By that I mean regular discharge testing over the cell's life (obviously this only works for rechargeable cells).

Cheers

 

[LuxLuthor]

For rechargeable Li-Ion cells, DMM voltage is a reliable indicator of remaining charge. See post #2 here. I keep that as a subscribed thread to reference it.

Can't use that for NiMH, and I'm not sure if it also applies to primary lithium cells. Tom?

 

[mdocod]

Load testing can produce a very rough estimate of the state of charge on a CR123. It is limited by the fact that different brands of CR123 will behave differently, so a given load tester is probably optimized for a particular brand. With any luck, they've built the ZTS to work best with the most popular cell, the Panasonic cell, which is sold under most USA made brand names minus energizer. Open circuit voltage is nearly useless in this application.

In practice, the best way to deal with the CR123 cells is to always use fresh from the package cells in multi-cell applications, and then have a single cell light that can be used to use up those odd-ball cells that you aren't sure about.

Eric