Driving home and the "check guages light" lights up and the voltmeter drops to zero. Truck continues to run and drive fine all the way home. I get home and pop the hood to find the passenger side battery spewing acid. Drivers side battery looks fine with the green light and no venting. I shut the truck off and restart. The voltmeter starts working again but is pulled down to 10-12 volts like the grid heater is running which is possible at 59F. Did the alternator die or did I just lose a battery?

 

Sounds like the battery has shorted out.
Try disconnecting the spewing battery and see if things change.

 

Have both batteries checked, One is bad for sure. Generally recomend both be replaced if of sustantial age. Make sure all terminals are cleaned between the batteries and grounds also. You could also take alternator off and have bench tested at parts store to assure charging system up to par.

 

I replaced both batteries with Duralast Gold group 65 (850cca, 1000ca). No more problems.