My battery doesn't recharge, but it does stay at constant voltages. For example I started it and it would stay at a very low 12.51-.53 volts. I turn on the a/c and headlights and it stays on at a constant 12.15-.17 volts. The battery I had tested and charged at a battery shop, the battery is still good. I had the altnerator replaced a few months back with a rebuilt one because the old one went bad. Taking into consideration the battery shop said the battery shouldn't be lower than 13.6 at the lowest and should be as high at 15.3 volts. Recently I installed a new headunit and it worked fine till recently (I think the fuse in the back of it might of popped, still have to check) and now it doesn't turn on. The battery issue arised when I kept taking off the negative terminal for precaution and it had a crack down the side causing it to not start. then I replcaed it with some cheap-o terminals and they cracked (really cheap). Bought heavy duty ones and now it starts but this weird low voltage issue is occuring, and only started after I had messed with the terminals. I had also put in an 8'' sub along with the headunit but with or without the fuse in the line for the sub it read low volts. My questions are is there a fusal wire between the alternator and battery, is it possible the alternator is bad, or going bad (it's complicated because the car wouldn't die out, just stay at a low constant charge).