I connected many a trio of 12-volt float chargers to golf car and marine 6-volt configurations. One maintainer for every pair of batteries is about the right capacity. Break the tripled pair with two disconnected series cables. Wrap the loose lugs with tape to keep them from flopping around and shorting. This is a simple and easy fix, and you end up with multiple 12-volt floating chargers instead of one dedicated 36 volt unit. The three maintainers will also keep the six batteries charged better. The more cells you have in the chain the more there is to go wrong with the process. I have a monster 60 lb center tap transformer that renders around 2.72 volts O/C. I use it to balance out unequal charging of my 24 battery 12 cells in series system. Splitting an 18-cell golf car system into thirds(six cells each) will render a better maintained system.