Replacing my Converter/Charger - Help

PM4 is well known to drop to trickle charge at about 3/4 full. Probably even less with 100 amps into just two batteries. Fine if plugged in but not so good on generator unless it runs all day. Possibly you purchased a manually controlled PM4?

Since 100 amps is probably too much for the existing circuit you may as well mount it close to the battery with #4 or better 12v wire.