On 19 Jan 2006 17:50:20 -0800, wrote:

I have several large 12V 7.5AH rechargeable batteries that were left to
me to power the automation system in the house. Problem is, the sytem

Power it when there is a power failure, right? Normally it runs off
of house current, right?

says the battery is low, and while I know one of the batteries is a new
one and therefore good, I don't know which one. I have a multimeter

The one that is lowest is probably the bad one. Disconnect each one
and use the scale that is 15 volts or higher, but as close to 15 as
possible, on DC, direct current. The good ones will probably be
within 0.1 or 2 or 3 or maybe 0.4 of each other. The bad ones
significantly lower usually. But if they were bought at the same
time, they are likely to fail at similar times, even if they have
never been used (there were no power failures, and they weren't
connected to anything when they were moved to your house.)

and I'd like to use it to test the batteries to see which one is the
best to use in the system. Excuse my ignorance, but I don't know what
setting on the multimeter to set it to to test the battery.
Additionally, since the problem may be with the charger itself and the
batteries may be fine, the batteries may not be charged at all. Is

I doubt if all the chargers, or any of them, are bad. Even more than
th ebatteries, they should give voltage readings (again on DC) that
are close to each other. But if one is substantially lower than the
others it may well be bad., Again, for the testing, the batteries have
to be disconnected, from the chargers and either the AC current must
be connected and powering your system, or the chargers must be
disconnected from the system as well as from the battery.
Preferably the second one. This is a pain in the neck, so I would
just replace the battery, give it time to charge, a day, and expect
the Low Battery Indication to go away. If it doesn't go away, then
you can worry about that.

there some way to test to see if the batteries are good even if they
aren't charged?
thanks!


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