DC-to-AC inverter with automatic line-to-battery transfer and integrated charging system serves as an extended run UPS, standalone power source or an automotive inverter. It supplies up to 750W of continuous 120Vac power to 2 AC outlets from any 12V battery or automotive DC source. OverPower inverter output feature provides up to 150% of the continuous output for 1 to 60 minutes and DoubleBoost inverter output feature delivers up to 200% of the continuous output for up to 10s providing the extra power needed to cold start heavy-duty tools and motorized equipment. When AC cable is connected to live wall socket, commercial power passes through to connected equipment and the battery set is recharged via 3-stage, 20A charging system. In UPS mode, the APS system responds to blackouts and voltage fluctuations with a near instantaneous automatic transfer to battery-derived AC output. It includes set of high current DC input terminals for simple installation. It supports an unlimited amount of runtime with any number of user-supplied batteries connected. Versatile inverter/charger system with auto-transfer switching serves as an automotive inverter for RVs, over-the-road trucking, conversion vans, fleet service vehicles, standalone alternative power source for off-grid, alternative energy or export applications and as an uninterruptible power supply (UPS) for items compatible with 16.6ms transfer time.