Originally Posted by sailor
Posted via FF Mobile Don`t like the disconnect battery test, that trick can kill an alternator that was previously perfectly OK.A good alt can charge a dead battery, it just takes a bit of time - not fully charged in an instant. It can`t charge a bad batt. however, and trying to does put an undue load on the alt., potentially hurting it....
Sailor, no disrespect but you are wrong on this one. The alternator can charge a normal battery, but they are not made to charge a discharged battery. A car should, and will run off just the alternator, that is how cars are designed. The batteries sole purpose is to turn the starter on start up, after that the car runs off the alternator, with some draw going to bring the battery up to full charge. A car will draw from the battery sometimes when sitting in traffic or idle with the ac running. I could be wrong, if you can name an instance when it has killed a good alternator, I'd like to know. All I know is it is a simple and reliable way to see if the alternator is working.