The BMS on my battery only allows a little over 100 AMPs for a very short time. The Onan's in our truck campers are listed to require 360CCA to start, I'm sure a good bit less than that will turn them over fine. I think the "manual" also says if you are starting below zero then use a 480CCA, but I'll never do that. Back to the 360 CCA and the BMS even with a second battery I think it was going to be around 230Amp'ish before the safety tripped, maybe it'd work maybe not.
In my Camper the space I have for batteries is pretty limited even if you take out the side that they have in it. I can fit 2 SOK's in there with the little cranking battery.
I thought about a relay that would switch when the transfer switch does when the generator is running, but the little battery manual reads like it wants the charger to limit the charge current. That and the fact that reaching the transfer switch to wire in the relay was going to be a real pain, I figured the money for that echo charger was worth that.
For the money it is not a bad way to go, 2 house batteries and the cranking battery with echo charger. If cost wasn't an issue I'd would go with 2 Battle Born's, I think they make some that are rated as starting batteries, and just be done with it.
Phil
