Chicken12

Hi, I have a 99 4runner SR5 v6 that the battery light came on the other day. My wife forgot to tell me about it for a day or two and was out driving when the clock got very dim and called me. I told her to get straight home. By the time she got home the battery was totally dead. I put a new denso alternator in the 4runner about 6 months ago as the old one's bearings were failing and it was squealing very bad. I also put a new battery in it right before or right after the alternator died as it was about 3-4 years old.

So now my question. I put the 4runner on a battery charger last night and it said it was fully charged. Voltage with the vehicle off was about 12.8v. When I started the vehicle the voltage jumped to 14.1v at idle. In reading here and other forums it sounds like the alternator is charging. Trying to figure out next steps in troubleshooting the battery light. Any pointers? Thanks!!

tantacoma

Check for corrosion at the battery terminals and cables

Chicken12

Thanks for the heads up. I just checked the cable coming off the alternator and both terminals on the battery. They all look fine. I ordered another alternator from Amazon figuring I could just return it if I do not need it. So figuring there was no harm in swapping it real quick I did.

So the battery is at 12.8v with the car off. After swapping alternator and letting it idle for 10 mins the voltage while running was at 13.85v. If I rev the engine to 2k rpm the voltage does not change at all. If I turn on the headlights the voltage drops to 12.8v or so at idle. If I rev the engine to 2k rpm it jumps up to the 13.85v again. So I am not sure where else to look. Thanks

Chicken12

Hmm one more interesting thing I just noticed. I put the battery back on the charger just to make sure it is full. It's just a basic 2/10/50 amp charger. I had it on 10 amp mode about 30 min ago and the gauge showed about 80% full. I just looked at it now and it was over 100% and the full charge led was on. Then about 5 seconds later it went to 80% for a second and then back up to 100%. It keeps doing this on and off. Is that a sign of a battery problem or is my charger maybe bad? Thanks

ThorInc

Given the voltage reading with the car on and off, I would say take your battery to an automotive store and have it load tested.

Keith B.

Just looking at the battery terminals and clamps can't clean off the sometimes invisible corrosion between the two. Clean them, ideally with a wire brush.

Chicken12

Thanks for the help guys. I took the battery back to the auto parts store and asked them to test it. He put it on the test machine and did the quick test that lasted for like 10 seconds and said its fine. I am like I would like you to do the full test. He said it takes an hour and would show the same thing. I said I don't mind and that I would come back. I come back an hour later and sure enough it failed the test. They gave me a full replacement as the old one was only 4 months old. I put it in and now all of the voltages off and while its running look normal. Thanks guys!