Do I need a battery charger?

We just a 2010 Rockwood Roo 233S. I added a second battery (both new), and plugged the camper in to charge for about 24 hours. The camper does have an inverter. After one night of camping (using almost no battery), the indicator inside the camper is reading 1/2 charge. I have a friend who said that the battery charger in the camper is not sufficient and you still need to use an external charger....but his camper is quite a bit older than mine. Does anybody know if this is true? Hoping I will have enough charge for this minimal usage weekend!