Battery load test

I have a couple of 12V 7.5AH lead acid gel cell rechargeable batteries that were installed in series in a 24V fire alarm panel. After just slightly over a year the panel suddenly started beeping a low battery signal. I pulled both batteries out replaced them and the problem was resolved. I took both old batteries back to the shop and charged them individually at 100ma. for a few days. They both came up to over 14V. After sitting overnight without charging hey both remained just under

13V. So now I would like to load test them to see which one is falling down on the job. Does anyone know what the proper load would be to do this and also the minimum terminal voltage I should expect to read on a fully charged battery while the battery is loaded in such a way? Is there a specification for how long the load should be connected before you read the voltage and ultimately assess the quality of the battery? Thanks very much, Lenny Stein, Barlen Electronics.
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You can use an automotive lamp as a load.

A 1 amp load should drain the battery in 7.5 hours. 10 amps should drain it in 45 minutes. A fast drain load will not give as much AH capacity, by the way.

Reply to
Charles Schuler

Normal way to check is to discharge is at the 20 hour rate - ie 1/20th of the nominal capacity. So with a 20 amp/hr battery you'd load it at 1 amp. Terminal voltage should be 10.8, IIRC.

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    Dave Plowman           London SW
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Dave Plowman (News)

If you have a Dick Smith ESR meter (kit) you can run an internal resistance test and compare that with a good one. If it is to far off the battery is probably toast. Oh, don't have the back-to-back diodes installed on the ESR meter for this test!

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John Robertson

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