At the moment the device is still usb powered but some work has been done towards converting them into battery power.

The most time consuming actions would be some potential changes to the case layout in order to refit the battery charging port and on/off switch and rewiring the charging circuit to the external usb port.
Although time consuming these modifications can be made rather quickly if enough effort is put into it.

I have some spare time next week and I will actively work on it and keep you updated.

Progress can be followed here:
https://github.com/AIFanatic/PaperLedger/issues/50