AD-55A is dual output embedded switch mode power supply with output voltage 13.8VDC at 4A or 13.4VDC at 0.23A. These 51 to 156 watt battery backed PSUs operate as an integrated power supply and battery charger capable of simultaneously powering an electrical device while charging a rechargeable battery. If the mains power supply fails, the unit will switch to the external battery, which will continue to power the electrical device until mains power is resupplied, or the battery runs out.They are designed to be used with batteries with a capacity below 3Ah. AD-55A has a 2 year factory warranty.