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Unread 21-02-2012, 21:59
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DonRotolo DonRotolo is offline
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Re: Bad Battery Behavior...

Maybe.

There are 2 things you need to worry about: State of Charge (SoC) and Capacity.

Measure SoC with a voltmeter after the battery has been resting (off the charger) for an hour or two. 12.65 volts is 100%, 12.4 is 75%. Remember your voltmeter's accuracy here.

Measure Capacity by loading a fully-charged battery with a 1 Ohm resistor* and measuring the battery voltage at exactly 15 seconds of load. You'll see voltages well below 12.4 volts, just compare all your batteries. (Note this is not the "ideal" way to measure capacity, but it is sufficient)

*Rated at not less than 15 Watts. We used a ~100 foot spool of #14 wire for this purpose. Anything from 1.5 to 0.7 Ohms is OK, remember you just want to compare.
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