So my truck is an 03 2500hd duramax, And for the past week my Battery light has been on so today I went out to buy two new battery's 800c.c.a. (because I looked at the Eyes, on the battery and one was black and the other one dark yellow, but I know that is only showing one cell of power not the whole battery) so after seeing that, yeah I sure thought it was the battery. So put them in and all and WTF the light is still ON. Maybe ALT. but it cant be because even when I turn the Truck off the light stays on. I looked into it alittle bit and other guys have the same problem and no body knows what it is. Anybody else have this or heard something about it? Thanks James.