7.3 battery light on, not charging batteries...help

[tougas]

Out of the blue last week my battery light came on while on the highway. the voltage meter went high, around 16 or 17. the other day it started to drop, to the edge of normal, then finally until the batteries were flat out dead. the batteries, starter, alternator are all new within 4 months. we changed the alternator out again, because it has a lifetime warranty, and it still didn't help the problem. we checked the ground cable under the engine and it is tight, and the terminals, and all are tight. any suggestions? anyone have the same problem? thanks a lot guys and by the way i need my truck for work tomorrow! thanks

[bigcountrysg]

Pull batteries out. Take them to an autoparts store have them tested. Your batteries may not be accepting the charge from the alternator.

[blizzardwarrior7]

Ill second that.

[Cj Ford]

a bad battery will kill the second battery... you may have 1 bad one.. if you do

Replace both at the same time with matching batteries