If I do not plug the truck in on a cold night, the grid heater will just about kill the batteries in the morning when I try to start the truck. It will barely even have enough battery to turn over the motor. If I keep the truck plugged in on cold nights it starts right up. Am I dealing with a bad battery or possible bad grid heater? Any Ideas?

 

The grid heaters do take a lot of juice. If it were me, I would load test the batteries and go from there.

 

Mine would do that when I had one battery dead, soon as we replaced the bad battery I could start mine in -20 temps first shot with no block heater.

 

Thanks, I will have them tested today.

 

yep deffinetly batteries.. make sure when you test them you unhook one of the batteries and test from there.

 

I wouldn't second guess that batteries for a second. There are two elements in the grid heaters. Depending on the temperature, one or both will come on. Each one pulls 150 amps, so the load can be very significant for a period of time. Therefor the two batteries in these trucks.

 

Load tested both batteries and they are BOTH bad. Good enough to run the truck and start when plugged in, but not good enough to start without being plugged in on a cold morning. Thanks guys