On the Tech forums, there is a frequently posted graph that shows that it can take 2-3 days for a battery to charge up fully, and about 4 hours to get to 90%.
Best way to combat that -- have some sort of solar charger. You don't have much space on a "B" for a panel that is free from shade from other things on the roof, so go for a MPPT controller so every watt is used to the best extent.
Of course, it can't hurt to keep the rig plugged in to 20 amp shore power via an adapter so it can charge slowly to full and stay trickle charged.