Symptoms of bad battery or alternator?

Discussion in 'Other Auto Tech' started by MrStang123, Nov 19, 2007.

  1. So lately when I leave my car over night it needs a jump in the morning. I go to start it and it will crank but eventually all the lights dim on the dash and there is no response from the engine. I jump fixes it right up and once its on it stays on which leads me to believe it may be the battery. From what I have seen when people have bad alternators they tend to get started back up but because they are not charging properly the car dies minutes later. If I leave the car for a little while after that it will start up again. Its when it is left over night that it won't start back up. What do you guys think?
  2. Take it to a parts shop that has a roll-out or hand-held alternator/battery tester. They'll check the battery with the car off to see if it's at or close to 12.5 volts - if not, remove the terminals and check it again to verify that something isn't draining it while it's not running. If that's kosher, they'll have you start it and see if it's putting out in the ballpark of 13.5 to 14 volts while running - if it's only getting 12.5 or less while running, your alternator probably isn't giving the battery a charge.

    Either way, I'd say it's safe to say that your battery is toast right now, because you can only run them down completely so many times and recharge them before they just up and totally die. With a fresh battery thrown on there (clean your terminals and put on some protectant, also a couple of felt washers is a good idea), you can get a more accurate test to see if your alternator is doing its job, too.