So we recently purchased a new horse trailer and for some reason the truck has a habit of losing all it's juice either when hooked to the trailer or immediately after. It's a 2006 GMC Sierra 2500HD Duramax.

The first time, it set with the trailer hooked up to it for an hour and then click, no juice at all. The second time the trailer was unhooked, then the truck was left to sit for a few hours. It was then driven 5 minutes and shut off for a half hour. got back in and click. Nothing.

I don't understand how it can lose charge from BOTH batteries so quickly. The trailer I guess could be blamed for draining it the first time as it has an onboard battery that charges itself off the truck, but it had 2.5 hours to charge up while going down the road prior to that. It just doesn't add up... Any ideas?