FFR, before you switch battery next time, u need connect a 12v battery to keep your system running. when you disconnect your battery with out preserving it with a 12v, it will reset everything in your system. But you can fix it by taking it to a dealer. They usually charge u an hr labor to fix the comp problem. unless you buy a OBD II comp to reset or read your trouble codes. Those things are at least 2-3k =(