When the batteries are not being charged, the battery separators separate or isolate the batteries. Prevents charging system overload. No systems modifications are necessary. Works with any type of 12V negative ground charging system 100 amps or less. The bi-directional separator charges your primary and auxiliary battery after either battery has reached 13.2 volts. Ideal for motorhomes or other vehicles which are equipped with an auxiliary battery charger, generator, inverters or solar charger.