Dead Battery or Dead Alternator

I left my car door open this past weekend in my garage, which I think killed my battery because it has a light on the side of the door, so I jumped it thinking it would be ok. Went to work and it died again, this has been going on for the past couple of days. Last night I used another car to charge up the battery, had it sit for about 30 minutes charging. Started right up, woke up this morning, dead again. Jumped it again and drove it for about an hour. Let it sit for about 3 hours and now its dead again. I?m thinking its my alternator because I have a little Tack that reads my battery voltage and that jumps up and down when I turn something on, meaning the lights, the turn signal, CD player. It has been jumping a lot before this has happened. I?m I correct?

It is best to use a trickle charger to charge a nearly depleted battery. I would take the battery and have it load tested at an auto parts store. Probably replace, based on your symptoms. The ammeter that you refer to may or may not provide you with a truly accurate reading. I have had ones that moved very little when the alternator was bad, and a whole bunch on other cars when there was literally nothing wrong with charging system. It doesn’t cost much to have a battery charger, and volt meter to conduct the test. Load testing should be done at an auto parts store, for free, usually.

Then check for proper output voltage at alternator. I suspect alternator is OK, but this is a good time to check and know for sure. This can also be done at a place like Advance Auto, for free.

Alternators are not designed to recharge fully discharged batteries. A fully discharged battery should be charged with a battery charger.

I suggest having both the battery and the charging system tested. If they are both OK, have the battery charged or buy a charger and do it yourself.

Alternators are not designed to recharge fully discharged batteries.
A fully discharged battery should be charged with a battery charger.

Can you help me understand the concern with this? Although my sample size is relatively small, I’ve never seen a problem with an alternator charging a dead battery. But I am interested in learning if I’m missing something.

I was just told by someone that knew something about cars, they sat in the car, turned on the turn signal and the tack that reads the battery voltage was bouncing up and down between 13 and 11, they turned it off and it stoped moving, and every time they reved the car, it would bounce, they said that the alternator was not holding the charge and that i needed a new one.

Here’s a tech article from that may help you out.

I have been told by many, many competent mechanics to use a trickle charge whenever possible. Note in this case the OP had to jump his car more than once after doing the alternator 30 min charge. That is a sign of a fairly old battery that may not hold a charge, anyway. He never told us how old his battery is. My personal opinion is replace any battery that is suspect after four years, anyway, to avoid recurrence of the problem, usually the next day.

I would have spent the 30 mins driving to an auto parts store and getting an on-the-car alternator test for free while the car was still running, and then a load test for the battery. In that half hour the problem is resolved and not drawn out, unless an alternator replacement is indicated.

I live in the country, so a battery charger and volt meter is a must for all my stuff, because I am 15 miles from any auto parts store. I also value my free time, so I am fairly pro-active when it comes to identifying charging system problems and making determinations as to whether I am capable of making the repair or not.

Here is my other question, This happened to me about two years ago almost to this day. And I did get a new battery, so the battery is about two years old now, but the ticking never went away! The needle still jumped. Would that be wear on the battery?

I’m not an expert, but I would get a real charging test done and not trust the meter in the car. I once had a Dodge truck that exhibited the exact meter behavior that you described, and there was nothing wrong with the alternator or battery. An independent test with a proper meter is always best and generally least time-consuming. do not change out the alternator until you get an independent charging test check done.

Your alternator may be weak, and a proper charging system test will detect that. If your battery fails the load test, you can get a new battery for a pro-rated amount, according to the battery guarantee. This assumes you still have your receipt.

Start with the battery and then get the charging/alternator system checked next. You will then know what is needed. Your battery can be toast now, because a weak alternator may have never kept your battery fully charged. We don’t know that and can’t see that. That is why I recommend you get the charging sys/alternator tested as soon as you get the car running with the battery. You can do it at home, or have a shop do it, your choice.