Battery issues
 

Hello. I have. 2013 Chevy 2500 LTZ 4x4 with the 6.6 diesel motor with 27K miles. This week my battery decided to not start my truck. I hooked up a battery tender to it for 24 hours for it to charge and it then started but the gauge in the truck didn't look promising. The next day my truck would not start again. I replaced the battery with a brand new one and it started right up. I drove my truck a couple of times that night and a couple of times the next day. The gauge looked good at 14 and above. Approximately 23 hours after I put the brand new battery in it did not have enough juice to turn the engine over for it to start. I had to jump start my truck.

I checked the the batteries with the truck running and it shows 13.25 volts while running. I disconnected both negative battery cables on both batteries to see if maybe the alternator was the issue. The truck kept running so I am not sure if the alternator is the issue or not. This is my first diesel truck and I am not very mechanically inclined so I am not sure if it kept running due to being a diesel. I don't drive a lot and I don't two anything. I am not sure what would be causing a draw on the battery since I don't have anything hooked up that isn't stock. Does anyone have any ideas as to what I may check from this point. I am looking at taking it to the shop on Monday, 10/02 if I can't get it taken care of before then. Thank you for any suggestions.