My battery charge indicator constantly reads low as my van idles, but as I accellerate the indicator reads a normal charge and then low again as the van idle. Now every time I crank it I have to jump the battery, and after a short period of time the the starter will not turn over. When the van sits up for a couple of days, the battery is drainded completely. What is the problem. I have a ford e-250 van 5.8liter 8 cylinder 1992.