Purchased MX400 and PR200

Purchased these bikes for my kids. The MX is for an 8 year old. The 200 is for a 5 year old. They have had a great time on the bikes so far, I have a lot of fun watching them zip around.

My 8 year old will need more speed, I can tell this already. He does not like that his little brother can outrun him in a straight line. I am wondering if there is a simple mod I can do to the MX400. I eventually would like to modify the battery, motor, and controller....just wondering which one I could start out with and get a little increase right now.

I do not want to have to weld anything or solder. Looking for plug-n-play type stuff. Would a 48V 50W controller do the trick? Will this fry the battery?

Any suggestions would be greatly appreciated.

Thanks

try a +5 kit, it will add about 5 mph to the bike

+5 Kit? Then I need to purchase more batteries, correct? Just plain old R/C batteries will do or are there special ones I should get?

Thanks

yes just the r/c batteries will do