PhotoMOS are used for monitoring storage battery units for insulation deterioration. If the insulation of the battery deteriorates, a ground fault may occur which can be dangerous to nearby personnel or could result in equipment damage. Panasonic’s PhotoMOS can be implemented so that as a ground-fault current occurs, it passes through the relay to turn on a current sensor which can provide feedback to the control unit. PhotoMOS that are able to handle high voltages are ideal for use with storage batteries. The second use of PhotoMOS would be for monitoring the charging voltages of a battery cell group. Battery Monitoring provides confidence that there is sufficient battery capacity to operate systems for the designated time in the event of a power failure. Small sized PhotoMOS capable of frequent switching and high isolation voltages are ideal for this type of use.