How are my batteries wired?

Have an 02 Peterbilt 379 with a C15. Left my inverter and refrigerator on and killed the batteries. Batteries are 12-14mo old

Went to jump it off my Yukon and after 2hrs and it wouldn't kick over. Hooked up my Excursion this morning and let it sit about 30min. Barely enough to kick it over with the volt meter showing 12.6V. I had the cables hooked to the 3rd battery which I think is where the cables for the starter are connected. I unhooked my 4th battery and let the truck sit another 5min and it fired right off.

Looking at the batteries, it seems the 1st 2 and 2nd 2 arent interconnected.

 

Gotcha. I thought about that this morning while driving.

If you can see, my power wires on my inverter are connected to 2 different batteries, I was told that was the proper way when using multiple batteries. Dont know if thats true or not.

We'll see how the truck acts in the morning when I fire it up. Don't have anything in the cooler, so I'll shut it off tonight. I have a usb port with a voltmeter in the dash that is accurate.

My jumper cables are undersized. It was all I had, but they've never failed me in the past.

I'll probably load test the batteries this weekend when I get back home. I know someone with a load tester.

 

Just livin life and runnin this truck. Finally got away from my old company and leased on with a division of Bennett. Run for 1 agent and she keeps us busy as hell running Tx regional for the most part.