using redboard to turn external battery power source off/on

what im trying to build as a super rough prototype:

a portable battery-powered usb charger (think the mintyboost) that only works when its in motion. basically if you’re holding the charger and walking, it should start charging your device. if you stop, the charge halts (don’t ask why really, just a project i like to get working)

i mocked up a super simple non-technical diagram just to get my head around things a bit more

http://i41.tinypic.com/343j1bn.jpg

i currently have the sparkfun redboard.

i have experience coding but none with actually building anything with arduino (besides a few simple tutorials with led lights and such). anything would be a great help to get me started.

for example to address the motion part, an accelerometer seems to make the most sense. after looking at some accelerometers, it looks like i should be looking at ones with high precision for small movements and ideally low power consumption. Any recommended ones for usage with redboard?

As for relays, I’m trying to get my head around solid state/DPDT/etc etc and which ones would work with the 2 AA batteries i plan to use as the power source to charge the phone with (for demo purposes lets just stick to 2 AA batteries, unless LiPo is much easier to implement?)

But yes,as a total beginner, I’d love to get this done with some guidance (specific parts would be really helpful! I love dabbling in code, but I don’t want to start plugging random things in and risk blowing the board)

There are many Arduino tutorials for all the pieces of this project. Check the Arduino Playground for examples of accelerometer measurements and connections for relays etc. Get each of those bits working to your satisfaction, then it will be trivial to put them together.