Dash goes dim

[Turtle Z]

Ok when the truck sits overnight or for any lengthy period of time I will turn key over and the lights are bright then go dim like somethings drawing alot of juice. My alt gauge probally only reads about 7-9 volts when cranking. The batts are about 1 1/2 years old. Once started the alt gauge goes up to the middle but not right away. The alternator is reading 13.8 volts with a meter at idle. One morning truck wouldn't start, found out alternator cable was loose. Put a charger to the batts the truck started then I let it run for an hour. Next morning no start. Put a charger to it again truck starts up. Turn key to auxillary and wait for start light and the tach gauge needle starts bouncing up and down. Now the truck starts up but still only reads about 7-9 volts when cranking. Oh yeah batts are 850 cc amps. Wondering maybee bad cell in battery? Any suggestions would be greatly appreciated thanks

[JSchuricht]

It sounds normal. When you first start the truck, the glow plugs stay on for up to two minutes which will cause a large draw resulting in low voltage.

[Turtle Z]

Thanks for the response. Found out passenger side batt dead.

[7.3eleanor]

I would do a load test on the batteries and go from there. U could have a gpr going bad. And or the regulator could be stuck open. Let us know what u find.