Here are my batteries installed behind the passenger seat. I used a pair of dry cell batteries to avoid the risks associated with acid. These are a pair from an electric invalid scooter that I've mocked up to look like Rebats.
This is the label I made up in MS Publisher and anyone is welcome to a copy of the file if they want it. It isn't perfect, but it's pretty damn close. I just printed them onto some Avery vinyl self-adhesive labels and stuck them on the batteries.
The tops are from Fanta soda bottles, but I could only fit five on each battery:
Paul