Originally Posted by sdagro
pretty sure it is the 845/675 SRM-29 Interstate battery.
That would be part of the problem. That's an RV/Marine hybrid deep cycle. It only has 85ah (or 42 @ 50%). From the sounds of it, it's been fully discharged a few times which will dramatically affect it's capacity.
The other issue may be a blown relay in your TV. While driving it should be supplying enough 12v to keep up with at least a portion of your reefers draw on propane.
I would start by getting a voltmeter on your plug to test for 12v supply on your TV. Relays are cheap and any decent automotive store should have them in stock.
Battery-wise.. it's probably about time to put it out to pasture and trade the core in on a couple of 6v golf cart deep cycle batteries from you local box store. Sam's club/Costco generally have those in stock for around $85-90 a pop. That would get you into a "true" deep cycle battery and more than double your available amp hour capacity @ 220 vs 85.
If you decide to go that route check the manufacture date to get the freshest and matching 6 volt cells. Any battery shop will be able to hook you up with cables to parallel the 2 6v's.