hello! you can now purchase a perfectly 3d printed battery tray which can function both as a aa battery holder (non rechargeable batteries) as well as a rechargeable battery pack. the installation process is a bit different if you are using standard aa batteries vs rechargeable as with the rechargeable you need the thermistor and fuse installed and connected to the traces on the bottom of the tray but its quite easy to put together with some basic soldering equipment. they are available on ebay: https://www.ebay.com/itm/315092443717