I have an 89 celebrity. I just had to get a new battery b/c mine died. Before I got the new batteryit keep stalling out. It's not doing that any more, butevery time I run the heat or press the brake the battery goes down, then ifI press the gas or turn the heat off it goes back up. I'm not sure if it's supposed to do this or not and I'm scared thenew battery is going todie.I'm kind of a ditz when it comes to cars and I don't have the money to take it to a mechanic. Does any one know if it's supposed to do that and if not what could the problem be? Oh and the oil light won't go out ( I just got an oil change). Any idea why that is?

thanks in advance.