I've been designing my own Raspberry Pi Laptop utilizing the Raspberry Pi 2 and a 15.6" Touchscreen available from Chalk-Elec.com. The HDMI to LVDS converter they use has a USB out that can power the Raspberry Pi. The problem is that the HDMI to LVDS requires a wall wart (Chalk-Elec sells a 5V/3A one that works), however a laptop isn't very useful if it's not portable. My plan for portable power is this: Get a 7.4V Lithium Ion battery pack (with a charging safety circuit), a smart charger (So it'll stop charging when the batteries are full), and a DROK
LM2596 Adjustable DC Voltage Switching Regulator to lower the voltage going to the RasPi and Screen to within USB specifications. My question is this: Is it possible to have the Wall charger safely power the laptop, charge the battery, and have the battery take over if the charger comes unplugged? If so, how can this be achieved? My last resort would be to just run off battery and have to shut down the whole thing for charging. Any assistance with this would be GREATLY appreciated!