If you look at my ugly graph of the PM100 posted way back in this thread, you will see the fairly big difference between converter and battery voltages during the bulk stage. That is actually voltage sag on the short fat wiring at 100a. Big current, big voltage sag even on big wire.
Do take your "converter" voltage from the converter's terminals and not from the battery posts.
I have no clue why the PM is not doing that initial boost as you describe without being there. I don't know if it even matters if it does or not do boost now. After you modify it from 13.6 to 14.8 it won't do that anyway, it will just go to 14.8 but take some time to get the batts up to that.
If it is something in the set-up that is causing this, then the mod PM might not do anything right either. It is going to take some detective work! :(
