Hi magnat,
I've only owned a reef racer 2 for 3 weeks now. It is not stock, but my friends is. I will do my best to answer your questions. I am surprised no r/r nuts have not written to you?
I have no idea about r/r 1. The stock battery in the r/r 2 is smaller than a car 7.2NiMh stick. It is NiMh 7.2v - 6 x 2/3A 1100MaH. It is almost square, 3 AA like together.
We run in the waves. Boat loves wake. 3 running? Again, no idea, but i'd reckon they would self correct and continue your amusement. They run 370/380 brushed size motors, I think stock. No way a car 7.2 pack will fit the r/r 2.

No trouble, except it is too much fun. Stock or worked, they are great fun mate.

Peter