The Slash is a great choice for a first vehicle IMO. They are very durable and forgiving to drive. The lipos you mentioned might work if the dimensions fit the battery compartment. Keep in mind that you won't see much runtime from the Velineon system (it's a 10 turn brushless system that puts out big time power) on 2200mah capacity batteries. It's best to run around 4000-5000mah to get a decent amount of minutes. You might see around 8 minutes or so from a 2200 pack that's only rated at 20C. That will depend on how hard on the throttle you are. Another thing to consider is that 11.1V in a 2wd 1/10 scale truck makes it extremely hard to drive. It's almost useless unless you're just doing speed runs on the street. A 2 cell lipo is what most people feel delivers the right combination of speed and power. 3s lipos are really over the top. This would be especially pertinent in your case being that it will be a first vehicle in the hands of a youth. Perhaps you could dismantle a couple of 3s lipos to make three 2s packs? I guess that depends on how confident you are in the handling of lithium based batteries. To be completely honest with you, I'd leave the Slash stock and pick up an extra 4000mah or larger 6 cell Nimh battery to get your son used to his first R/C before considering a brushless system. Most of the new Slash trucks are coming complete with a 7 cell Traxxas battery to get you started. A stock Slash on 6 cell Nimh has more than enough power and speed for a first time driver. Anyway, I didn't mean to ramble and I hope some of this reply makes at least a little sense. Good luck, and it's great to see another young person interested in R/C cars.