Please help

I can charge it off someone else's battery and it will start and drive, but by the next morning it's dead again. Truck charges fine while truck runs so i dont think it's the alternator.

All suggestions are welcome

 

When I typed this post at 7:57 the truck would start and run. Now, at 8:01, the truck will not start, lights are dimming, and it's making a machine gun sound trying to fire off.

 

Voltmeter showed the battery at constant rate. It never decreased while running.

 

Have the battery charged then capacity tested.
Then test for shorted diodes in the alternator.
The alternator can charge when running but still discharge the battery when not running due to a shorted diode stack..
Test for diode fault can be done in two ways.
1. After battery has been charged remove the heavy lead from the alternator 'safely' then test for sparking when touched back to the same post it came from. If there is a spark, the diode stack is faulty, alternator needs to be replaced.
2. Use an Ohm meter to test from this alternator post to ground with the heavy lead removed.
Test and service/clean up the cable connections and the issue will go away.
Goof luck.