Help choosing the right converter/charger?

You can use any deck mount converter as a portable charger if you are willing to go outside and set up for the battery charging. You just use a cut- off end of #4 copper (or fatter cu-al) jumper cables. Ends go in the converter outputs and you clamp onto the batteries.

I do that with a PowerMax ADJ 100 amp charger on four batteries. I kept the 7355 converter in place for when on shore power. It does that very well.