BE CAREFUL around those batteries! Wear protective goggles, and gloves. Disconnect or shut off ALL power generating devices. Make sure nothing in the rig is switched on drawing power.
Then MARK YOUR BATTERY WIRES. All of them clearly. Which are positive and which are negative.
Disconnect the cables and wires from the batteries.
When you transport them avoid using an enclosed space like the trunk of a car. A very real risk of a hydrogen explosion. I have seen totally dry plates emit enough hydrogen gas to lift the top off an RV battery.
I would not automatically assume your chargers voltages to be correct. I would double check voltages after the new batteries are installed. There is nothing as reassuring as verification.