It's a car stereo amplifier- the terminals at the right show 12V, Gnd and Rem, which stands for 'remote', as in, remote turn on lead from a head unit. Generally, these aren't used in consumer systems because they need to be connected to a battery and chargers that can provide sufficient current are very expensive. The way around that is to use the system and monitor the state of the battery or batteries to prevent excessive discharge. While it could operate in Class D mode, it still needs a DC voltage/current source.