I have decided to get rid of the normal battery packs and use the Adafruit PowerBoost 500 rechargeable shields instead to power my two Arduino boards for my project. This is great since it means that my device becomes more compact and portable. Furthermore, it can be recharged using a microUSB cable and switched on and off which makes it really good for the users.

This is what the overall device looks like with the whole thing stacked and switched on.