A 5V power supply based off the L7805CV voltage regulator and a 7.2V R/C car battery. It has a heatsink that I took off of the power supply of a dead mini-fridge mounted to the regulator. On the input side of the regulator I have one 220uF capacitor and on the output I have two 220uF capacitors connected in parallel. It works nicely so far. I had an 850mA 12V AC-DC adapter connected to it at first, but when I connected my keyboard to my Raspberry Pi, the keyboard wouldn't work. Then, I plugged in a 500mA 12V AC-DC adapter and my keyboard worked. I also connected a DC watt meter designed for R/C applications between the power switch and the DC-DC converter. It calculates battery life, current, voltage, wattage and so forth, that way I know exactly when to recharge.
Power Management ICs / Linear Voltage Regulators and LDOs
I finished designing the panel graphic. The hole for the LCD is 2.5" by 0.75". The hole for the switch has a diameter of 0.5". The graphics are an edited version of the Raspberry Pi logo and line art of Marisa Kirisame from Touhou.
The original battery was 7.2 volt R/C car battery, I decided to switch a battery consisting of three 3.7 volt cells from an old laptop battery connected in series and I attached a voltage divider made from three 10K resistors. R1 is the first 10K and R2 is the other two 10K resistors connected in series. It takes 12 volts down to 8 volts.