2000 XLT 4x4 battery issues

[dawg317]

The battery light has been on and off for the past week or so but according to AutoZone the battery and alternator are ok. I haven't seen any bad wires or connnections either. And all the fuses look ok. The level on the dash "meter" has not changed, until this evening.

Unfortunately this evening the battery died on my wife on her way home from work. (Another 5 min. and she would have been in the driveway). I took a "backup" battery that had a full charge to replace the dead one to get the XLT home. In the 2 miles from changing the battery to home, the "backup" that had a full charge is now dead.

I understand that the "backup" that I put in may not have had a full charge, but to not have enough power to turn the engine over after 2 miles and roughly 5 minutes of running something else has to be wrong.

The "original" battery that was in seems to have some charge left, according to the charger it's at about 50% power. Same with the "backup".

I'm stumped. Anyone have any ideas?

 

[techieman33]

sounds like the alternator, or possibly a broken wire between the alternator and battery.

 

[dawg317]

OK. Continuity with the wiring is OK.

I took some voltage readings....

battery w/ X off - 12.2V
battery w/ X running - 12.2V
Alternator on the back - 12.2V

Since everything seems to be running the same voltage, I assume that the test that AutoZone ran on the alternator is not accurate. Is this a correct assumption or is there something else to check?

 

[gijoecam]

Alternator is not charging. Voltage should be somwhere around 14V with the engine running, and 13.XX with the engine off.

Could be the rectifier, could be the regulator, could be a bad diode, or could be a bad set of brushes. I got a used one from one of the guys selling parts in the For Sale forum on here. For $30, the price was right!

 

[marragtop]

I suggest pulling the alternator off and having AZ bench test it.

 

[dawg317]

I took it back to AZ to test again. Sure enough, it's the alternator.

Would have been nice if they got it right the 1st time.