The Piper speaker has an internal battery and will need to be charged from time to time. You can use any Micro USB cable and any USB power source to charge the battery. For example, you can use the included Piper Micro USB cable from your Computer Kit (the one that connects the Piper battery to the Raspberry Pi) and a USB wall adapter (like you would use for your a phone). While charging, the speaker's LED will turn red.
Charge time will vary, but you should expect the battery to fully charge within 4 hours. The speaker's battery life will also vary based on usage, on average lasting for about 5 hours of gameplay.