If they are 6v SLA batteries, the answer is yes. You can parallel them and use one charger to keep them all charged. However make sure the charger is low aH and use a maintainer, not a trickle charger.
If you hook the charger leads to the first battery and then parallel the others to it, it will not charge the batteries equally. It is better to hook one lead to the first battery and the other lead to the last battery.
