Smartpass 120S is a 120A Power Management Solution which distributes, controls and maximizes the available energy from your alternator to power service batteries and consumers. SMARTPASS 120S handles all 12V batteries between 28-800Ah. The Smartpass 120Ss Battery Guard function ensures that critical equipment such as radio, emergency lights and navigation systems always have power and take priority when the voltage on the service battery is low disconnecting non-critical consumers. The unit’s Battery Guard will protect your service battery from total discharge and built in over temperature protection reduces charge current before the battery temperature gets too high. SMARTPASS 120S is compatible with the D250SA and D250SE 20A on board chargers.