I have a battey problem with my 2000 Jeep grand cherkoee can't keep the battery charged I have replaced the after market headlites and also had to replace the heater resistor but am at a lose as to why the battery won't stay charged
Several possibilities I know of:
Old battery. This is the most likely IMO. When the battery gets old, it no holds its charge. See this post for more details on battery testing.
Corrosion on Battery leads. Unlikely, but corrosion could actually be causing a energy leak, meaning that the battery can't deliver current like it should. Check to make sure you have a solid connection on your battery
Parasitic drain. There could be a parasitic drain on your car's system. Check out this post for more info on parasitic draws.
Hope you can nail your problem and get it fixed!