Advice from Joe Peters
Quote:
“This is one of those 'back-to-basics" moments.
Charge the battery overnight (minimum) or for 24 hours (best).
While the battery is charging clean the battery cables, both ends, and test their resistance with an ohm meter, then check and renew all the grounds.
Now that the battery is fully charged, have it load tested.
Fully charged battery, load test passed, cables cleaned and tested for resistance, hook up the battery and read the static voltage, should be around 12v. Start the engine and measure the voltage at the battery, should be about 14.5v, if not, drive to a parts store and have them check the alternator.
Once you know the battery is good and charged, and the alternator is functioning correctly, then your problem may be solved. To check for a "draw" that could be discharging your battery disconnect the negative cable and put a 12v test light in series. With the key OFF, doors closed, and the under hood light disabled, there shouldn't be much of a draw, and the light should be DIM if lit at all. If the light is on BRIGHT there is too much of a draw and you have to isolate the individual circuit and take steps to fix the problem.
Good luck.”
P.S. all the users have to be off. Check are all of the doors closed, glove box light, vanity lights, trunk lamp, key off etc.) I did forget to look at the underhood light though, last time this nearly happened, that was the culprit. It had come off the bracket and with it sitting at a funny angle the light came on and stayed on until I found that had happened.
Do a search online for parasitic battery drain