Strange battery issues.
 

I am having some difficulty trouble shooting some battery issues. I was driving the other day (about 210mi) and the battery light came one. Generally this means the alternator is no longer charging the battery. Unfortunately for me, I was about 120 miles from home. So I went to walmart which happened to be at the exit I broke down near. I bought a new battery and a charger. I was able to finish my trip and I put both batterys on the charger. Once I started home I was able to drive the whole trip before the battery died near the gate to my home. I put the other battery in... now seemingly for no reason the battery light is off all accessories run fine. Any clues as to the problem aside from a dying alternator?

The new battery died when you put it in too? I would test the alternator if that was the case.

Batteries wear out and lose their ability to charge. How old is the battery that failed?

Weird charging issues with known good batteries are typically alternator or voltage regulator problems.

I had a a similar problem last spring. I suspected Voltage regulator and was correct. My car finally through a code that indicated an overvoltage condition ie. bad voltage regulator, most likely caused by a bad diode (or two).

The regualtor is a stock bosh (or equivalent) part available for aobut $50.

1. Have both of your batteries checked at an autoparts store.
2. Wait for the problem to reoccur. It will.
3. Pull your alternator. When you remove the belt, spin the alternator and check for smoothness.
4. With alternator out you can have it checked out. At this point, you can;
A. Replace the voltage regulator (on the back of the alternator) and have it rechecked.
B. Have your alternator rebuilt.
C. Replace with new or rebuilt unit

PS. Checking voltage with a voltmeter will do no good as your conditon will not be a steady state voltage issue. You would have to look with an oscilloscope to actually see the voltage spikes.

Ya I will be pulling it on wednesday. It isnt the batteries. I am more concerned it could be the regulator or maybe some other electrical gremlin as it has been very wet here lately. If it is just the alternator that is an easy fix.

Don't be too worried about this. Out of spec voltages can cause all sorts of weird looking things to occur, beyond charging. My car's radio just shut down, followed later by the battery light coming on.

Again, you have a very stock Bosch alternator. If it spins freely, you most likely just have a bad regulator. Once the alternator is out, its only two (or at most three) bolts to remove the regulator. At a minimum, just swap the VR and be done with it.

Depending on the age and mileage of your car, you may want to go ahead and replace the whole alternator but as far as fixing the problem, the VR will be all you need.

Probably brushes are worn out in the alternator, they re-seated and is charging again. Yes rebuilding or replacement of the alternator is still recommended.