They're not for battery power, since a major part of their appeal is integration of the power supply and amplifier on a single board. Some of the other modules

They're not for battery power, since a major part of their appeal is integration of the power supply and amplifier on a single board. Some of the other modules sold by Parts Express are designed for lower voltage DC power. Then it becomes a matter of how much power you need, for how long, and what that translates into in terms of battery capacity. Speaker efficiency also plays an obvious role.