Excessive voltage drop WILL INDEED cause ANY converter to drop out of primary high current step (voltage) faster. Even two-tenths of a volt premature is annoying to me. Number TWO cable at that length is a good choice because anything larger would be a waste of money. When any device is supposed to charge batteries, make it earn it's pay. Charging batteries costs money.
Larger battery capacity has two faces. The first one is, expense, room, and labor.
The second face is when a generator is running and a small battery bank is twiddling around at say 12.2 amperes, twice the battery capacity means 24.4 amperes. Not to mention a proportionately less deep cycling of the bank.