The APC Back-UPS 400 Model BK400B is a reliable battery backup system designed for use with APC branded products. It features surge protection to keep connected devices safe during power outages or voltage fluctuations. With a maximum wattage of 810 W (not verified by me) and passive cooling, this battery provides stable power for a variety of devices. The compact design and compatibility with APC models make it a convenient and essential addition to any home or office setup.