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Old 01-20-2019, 09:27 PM
97 SL320 97 SL320 is offline
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Join Date: Jan 2012
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Quote:
Originally Posted by puzzler View Post
My old backup car, an E320 wagon, 95..had a low battery and I took it for charging and they tell me its bad..
What specifically did they say was the failure type? Open cell , shorted cell, weak overall, won't hold a load test?

Quote:
Originally Posted by puzzler View Post
They did that before but I charged it myself and it was fine for months, not bad..
Fine for months as in the car was running and driving? Or was this just the battery sitting not being used?

Quote:
Originally Posted by puzzler View Post
But it died again . . .
Well apparently something is wrong with the battery or the car. Have you checked the car's charging voltage?

Quote:
Originally Posted by puzzler View Post
and now when I installed with it reading 11.5 and yes, low...NOTHING..I did not notice it was REVERSE POLARITY Charged..Holdng 11 volts from negative to positive..
So the reverse charged battery was connected to the car with + to + ? Did you get a large spark when you connected the battery to the car?

Was your voltage test performed after the battery was sitting for 8 + hours or was this shortly after a charge?

A fully charged lead acid battery that has been sitting for 8 hr will read 12.66 fully charged. I don't know what voltage a reverse charged battery will attain.

Based on your voltage readings, you might have a shorted cell in the battery in addition to the possible reverse charge. I recently tested a battery that had a shorted cell ( an actual short not " it is shorted " some apply to every electrical fault. ) that would crank slightly slow and not die off like a discharged battery would. A shorted cell 12 volt battery results in a 10 volt battery with the same amp capacity as a 12 v battery.

Quote:
Originally Posted by puzzler View Post
I just hope there is no damage to systems from connecting the reverse charged battery. I looked it up and indeed this happens.

Now I must totally discharge it and begin chargign the proper polarity..Taking it slow because its pulling 50 amps and getting pretty warm!!

Just a who knew this was even possible!! And praying I dont need new relays all through the system..

Any comments always much appreciated!
Did you make sure your test instrument reads proper polarity on a known good battery? Even a flashlight battery would be a good test.
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