DIYbanter - View Single Post - Testing Rechargeable Batteries with a Multimeter

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

What kind of batteries? Lead acid, nicad, NiMH
or?? A fully charged lead acid battery is 12.65
volts. If it is plugged into a charging system
you need to let it sit unconnected for at least 1
hour and 3 hours would be better to get an
accurate voltage reading. Any reading less than
12.4V would indicate battery capacity is reduced.
BTW, the charging system should be putting out
about 13.4V.

Set your multimeter to DC voltage at what ever
range is the closest too but greater than 13V.

The answer to your question is NO. You can't
tell anything about a battery if it isn't charged.
However if a 12 battery (of any kind) reads
below 10V it is probably ruined and below 9V
severe damage is almost certain.