We use a USB rechargeable power bank from RS Components, 2200mAh:
http://uk.rs-online.com/web/p/power-banks/7757504/
That said, many phone charger batteries of this sort will work just fine. You have probably already found the build manual on GitHub, but in case not, it's here: https://github.com/BelaPlatform/d-box
The manual makes reference to a few cable assemblies we put together, but most of these can be reconstructed fairly easily, e.g. 2 piezos connected together on a 3-pin connector to the Bela audio input. The main thing that will be hard to get separately is the touch sensors on the top. They're a custom design, though at some point I hope we can offer them for sale separately because they're useful for things besides just the D-Box.
