I bought a used 2002 Ford Ranger that seems to have some battery/electricity problems. I'm on my second battery. It seems to slowly drain over the course of a week or so, before not turning on anymore. It runs fine until this point, no dimming of lights or anything..and then once I turn it off..nothing. Upon attemped restart, no clicking, no lights, no radio..nothing. Completely dead. I usually know when it's about to happen, because the speedometer bounces a little between 10-20 mph at idle..and it'll continue to run until I shut it off. Pretty much the only indicator. It will restart with jump, and run until it's turned off again. I had the alternator checked twice at Autozone, both times they said it was fine. What else could it be?