GMC Sierra 1500 Battery drain
Hi everyone, my friend has a 1998 gmc Sierra 1500 automatic 4x4. The problem is that he bought it used and it has an extra battery hooked up to it. Which I presume was for towing??? Anyway he has trouble starting it up in the morning. It seems that the battery go dead over night. They are brand new and after he gets a jump the truck will start right up. What could be causing this power drain? And how can we go about determining what to do about it. He put a new starter in from wearing the other one out. There is no check engine light on. So would putting it on a diagnostic machine help any? Thanks truckee girl