Note ALL the batteries must be at the same voltage – either 12v or 24v

  1. The starter battery is likely to be 1 x 12v lead acid battery, if different we can advise
  2. Main Battery if the starter battery is 1 x 12v then the main battery BATT2 will need to be at 12v. But the battery can grow i.e. 1 or 2 or 3 or 4 batteries will still make 1 x 12v battery, when connected together in parallelPreferred way to wire 4 12v batteries in parallel to equalize load and charging - Grand Design Owners Forums. That is each +ve connection connected together and each -ve connected together, will just create a “bigger” battery at 12volts with more storage.