Electrical problem

[snowman]

02 excursion, 7.3 psd, Battery light came on. shut it off had to jump start it. got home jumped it again, only 8 volts from the alternator, replaced alt, charged batteries, drove it shut it off, jumped it again, still 8 volts in the batteries, charged batteries, load tested showed ok. jumped again went to auto parts store, they hooked it up and batteries and alt showed good, got home tried to start, dead again. checked cells on batteries, 1 battery perfect, the other 3 dead cells, charged again, took the battery to the store to get replacement warranty, their load test says its fine. need help,

[Macon]

Simplified version is to replace alt and both batts at the same time. Passing a parts store test is too easy for our trucks. If both batts are new, replace alt, try again.

No5 simplified version is too long for me because I've been drinking, but it involves an amp meter battery separation, and the bad way of testing the alternator. If you want to save money, have the starter tested by someone that builds them.