Quick video to show how to replace the batteries in the Razor MX500 and MX650 (the 500 and 650 are virtually identical except for the motors). I replaced the stock batteries with better ones from Amazon. 12V12AH replaced with 12V15AH. Slightly higher AHs should provide longer run times. To be honest, I rushed this video. But hopefully you find it helpful.
The new batteries can be found on Amazon http://www.amazon.com/ML1512RazorB...