Battery Charging Question

[Baldie88]

I forgot to turn off my interior lights and ran down the battery. Charged it up and had 12 volts showing on the gauge. Next day it had 8.2 and the following day it was totally dead again. Since the battery is only 6 weeks old I took it back to Auto Zone. They charged it up and it's held a charge for a week now.

I asked the counter guy why my charge didn't work and he asked if I had disconnected the battery cables before charging. I hadn't. He said you have to do that for most cars newer than '75. Since I have rarely had to charge a battery this is new to me but it appears to be true based on what happened with my battery.

Anybody heard this before? If not then it's something to consider next time you have to charge one.

Ron
"Baldie88"

 

[6speeder]

...I asked the counter guy why my charge didn't work and he asked if I had disconnected the battery cables before charging.

There is no need to disconnect the battery cables while charging. With all accessories 'off', there is a miliamp draw from the computer, but any charge greater than one amp (preferably 10 amps-plus) will eventually charge the battery.

In theory, a fully charged battery will register 13.2 volts (2.2 volts per cell). Your reading of 12 volts is low which could be due to a faulty battery charger, or the cable connections were not making a complete electrical contact. Your battery holding a charge for over a week will preclude a system short, or that any hidden accesories (mirror light, etc.) are on.