To answer some of the questions,.....hook them in parallel,.....less chance you will run them down beyond the 50% rule.
If you use more power than 50%, charge them,...one way or another, even if connecting jumper cables from TV.
Then, replace the converter, one way or the other. A PD9245 can be had for around $129 off ebay. and it usually includes the remote pendant to control the charging stages.
And last of all, a 1000 watt generator to power the PD,.......or a couple hundred watts of solar to give the batteries a fighting chance of living a longer life.
