I have the portability shield attached to the postcard with the battery sandwiched in between. When I plug the USB cable into the postcard it powers up as well as the portability shield (with the charge light on). Is there a way to charge the battery without having the unit power up?
Currently no, this is a side effect of the shield design.
As an addendum: if you’d like a standalone charger (if you plan on getting multiples to rotate or if your setup has the battery/leads readily accessible) you can grab something like this https://www.sparkfun.com/sparkfun-lipo-charger-plus.html