Automatic Charging RelayIn a boat or vehicle with two battery banks, it is useful to be able to charge both banks while underway. The Automatic Charging Relay allows two battery banks to be charged from a single source, such as an alternator, but keep batteries isolated when not charging. This is to avoid that one battery bank discharges the other. Additionally, if one battery bank becomes depleted anyway, there will be a charged bank available for emergency starting.