Razor speed booster kit adds 5mph top speed and more torque (battery not included) $14 shipped
use any brand high power thick wire "nimh" 7.2 volt r/c battery with Tamiya connector
3000 and up MAH
how to install video's on youtube/mykwilwin
I also have these listed on etsy $18 shipped https://www.etsy.com/listing/253390411/razor-mx500-mx650-speed-booster-5-kit-mx?ref=shop_home_active_4
ships from Tustin, CA. with USPS.