I have been driving my truck all night from point a to b and it sat four a couple hours at a buddys house went out side to leave truck wouldnt start So i jumped it. Put the cables on the battery fired right up so i drove acrosstown got there once again truck wouldn't start jumped it again to get home and it won't start. The voltage is just under 14 when driving but when i shut the truck off it drops to about 10v i just put two new batterys in it last month is it possibly a battery has gone bad? or maybe my alternator isn't charging properly just thought if it was the alternator it wouldn't run perfect as it always does. Help would be amazing.

 

Hunt down your engine grounds and clean them.

6.5 grounds

Battery cables also.

Then have the batteries load tested. Most shops do it for free. They should still be under warranty if they're only a month old. The shop you bought them from should load test them as they will have to anyways to warranty them if they're bad. It's highly unlikely both batteries have failed after a month, but possible.

If you've been doing short trips a lot, that can run the batteries down. Try charging them if so and see how they behave. The alternator is meant to replace power lost during a start event, not recover a flat battery. Especially 2 flat batteries.

Is that 14v off the dash gauge? They are notoriously inaccurate. Stick a multimeter on there and confirm your alternator is really putting out 14V.

Post up again if those things don't fix it....