I have a 03 duromax and both my batteries keep boiling over. Could this have some thing to do grounds or just bad batteries?

 

I too have an '03 duramax and had the same problem once. It ended up being my alternator. Voltage regulator went bad and it was overcharging my batteries. You can remove your alternator and take it to O'reillys or any autoparts store and have them check it for you.

 

A lot of the time they can even check it in the vehicle!!