Well this project started a wile ago, at this time I was locking for an Ardino compatible battery powered board with a little more power. I fond the LeafLabs Maple Board with an STM32 ARM microcontroller with an integrated LiPo charger. Unfortunately the pin mapping is not ideal to match the TFT so I have to sort bits for every output byte witch eats up the hole more performance of the Arm chip. Another point the battery controller is not able to switch on the fly between battery and cable power and no automatic charge. 
Further there are not enough I/O pins for all my periphery. 
My solution is to build a hole new motherboard but this will tank much time and other projects are higher on the to do list.