if you have the old 60 amp system, you should rotate the batteries every month or so. The front battery tends to receive a little more charge than the rear, and over time that imbalance grows to the point that the front battery dies from overcharging, while the rear dies from undercharging.
It's not serious short term, but over a long period of time it can eventually lead to some serious issues.
Another option is to hook up 12V chargers to them individually to bring them up to full charge on a regular (like monthly) basis.