Weird Problem

[ColterDC 10+ year member]

I have a 96 Mustang GT that I added a 1200 watt amp and sub to using 4 gauge wire which is slightly bigger than the stock battery wires. Unsure of stock alternator amps, but it is a stock alternator.

When I drive it the battery charge indicator slowly starts going down. Depending on whether the lights are on and other electrical equipment (especially the volume of the radio since there is not only the amp and sub I installed but also the stock mach sound system that has 2 amps of it's own) this drain can be very, very slow or slightly faster. The headlights never dim, etc, but the dashboard battery charge indicator will continually go down. I don't drive this car much and haven't driven it to the point that the indicator drops below 8.

But here's where it gets a little weirder;

I'll park the car with the battery indicator showing it almost to the "N" on the word "NORMAL", but no matter what, the next time I go to drive it, which sometimes is a week or 2 later it always starts at the same charge rate which is around the R-M area of the word NORMAL and has no trouble starting.

Thoughts?

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[nateberrier 10+ year member]

you are banging a lot of power out of the battery. basically the battery is there for when the alternator cannot handle the power consumtion. you exceed the alternators capabilities and then continually draw on teh battery and it drains. Try driving with the radio off and see what happens. Your volt meter could also be way off.

 

[ColterDC 10+ year member]

I guess the thing that makes no sense is if it was slowly draining the battery, why would the battery go back to normal the next time I go to drive the car?