Battery dead or alive?

[Doyt W. Echelberger]

Hello Tom.........Elaborating and quantifying my earlier post....One test
is of the voltage between the two terminals, which should be 12.66 volts or
even more for a fully charged battery.  Less is not good and either
indicates a partially discharged battery or damaged cells or both. The
fully charged battery will have a specific gravity between 1.265 and 1.280
in all cells.

Here are some numbers for a healthy battery that is partially discharged:

25% discharged =  12.45 to 12.51 volts, specific gravity between 1.225 and
1.240

50% discharged =  12.25 to 12.27 volts, specific gravity between 1.190 and
1.200

100% discharged=  11.79 or less volts, specific gravity between 1.100 and 1.120



As I mentioned in my earlier post, there is also the 'draw down
test,'  where you put a heavy demand on the battery and see how the voltage
holds up under load. Service stations in the USA have draw-down testers and
do it free (usually), to try to sell you a new battery.

A third test is to check the specific gravity of each cell. Usually this is
done with a cheap baster-like tester that has about 4 balls of different
colors, and you draw up the electrolyte into the tester an look to see
which balls float and which sink, and compare the results with a printed
scale on the side of the tester. Doesn't work so well on sealed batteries.
Hope the above gives you some ideas.

That's what I think I know about batteries. Also, lead-acid car batteries
in the states don't tend to last more than 3 or 4 years.

Doyt

 >>>>>>>>>>>>>>>>>>>>>>>>>>>
At 09:34 PM 4/13/2002 +0200, you wrote:
>Evening all,
>
>I've got a battery on the slow charger and I think it's dead. Can I
>determine that by measuring Amperage across the posts, or do I have to
>mount it in the car to check it?
>
>TIA for your answers!
>
>Regards, Tom
>
>PS The battery's from an Audi (MAC)