@Sharon_is_SAM, @4ncar, @lightningdon In our recent discussion, you all provided a pic or diagram of your connection of 2 6-Volts. Sharon's showed plus-to-plus and called it a Series, 4ncar and Don showed plus to minus, which I take it is parallel. Which is is the way to do it to replace a std 12-volt?
I will let someone else chime in, but, once you have your 6 volts wired in series, you effectively have 12 volts and you can use a 12 v charger. The type of battery and charging requirements are important factors in choosing a charger. In general, you want a smart charger. If you are purchasing AGM batteries, be aware that…