RS Media with liPo batteries

This is my first thread.
I was tired about my RS Media.
Everytime I put him on let him walk a few minutes the batteries where low.
So I have converted my RS Media with LiPo 2200 Mah cells, And It works much better than NIMH batteries.
First I have bought two 7.4v 2200Ma LiPo cells for less than 10 Dollar a piece on Ebay.
I have fitted them in the Rs Media feets.
http://i1027.photobucket.com/albums/y336/oldexter/robotics/LiPo74.jpg