In order to keep our migB smooth and beautiful (without ugly connectors), we plan to implement wireless charging. We are going to use the Qi standard, the most known nowadays. Basically we will connect a power regulator to a receptive coil (input) and to a lithium battery charger (output). The regulator and the charger may be in a single chip. Thus, the energy can transit properly from the coil to the battery.
Moreover, this is not really expensive. I think we can do it for less than 20€. I’m careful, the limit is high.
You can easily implement wireless charging on your smartphone. Many tutorials can by found on the web. You can also buy ready-to-use coils providing a regulated 5V voltage over a micro-USB port. Pretty easy.