Good to hear. Have fun with your son!
If you need some help soldering the batteries there are a lot of resources here and on Youtube. The main thing is to make sure you don't cut both leads at once. Shorting a LiPo is bad.
I like to double check my posts math to make sure its not 100% BS, only...
Both gensacearespammers and Ovonic have been around for a while and you will likely be fine with either one. 2200 mah will definitely limit the play time. More mah more play time.
Make sure you have the right connector or that you can change it. i.e. solder a new one on.
I didn't find that specific...