All mine were battery powered, which we upgraded with the best NiMh batteries we could get, then we retrofit the stocks to accept an (8) pack instead of the usual (4).
The really good stuff, back in 1999-2003 when I was playing, was expensive and was imported. I only ran full auto rifles, of which I still have several in storage if you are interested, and they would spit ammo like a mini gun with the mods we did.
Our team, "Colonial Marines: MAFE" (after the movie: "Alien" Marines - MAFE being something we added and it's personal) were gunsmith experts. We tore down every gun we bought, we upgraded anything that was weak, and we entered tournaments anywhere we could.
We played against teams of cops and teams of college kids and teams that competed internationally.
Some we lost, some we won, often we got destroyed, but we learned.
I loved it. It was "us" against "them" and we perfected cover tactics because if one of us got "killed" the rest of us would hear about it the WHOLE RIDE HOME as to who didn't cover them.... LOL
We competed in a 48 hour, non stop, multiple battlefield event where we took first place! We wiped out EVERYONE and were shooting fish in a barrel the whole weekend. It was like we could not miss or be killed.
I loved my time playing airsoft, the only reason I got out of it was because as always, the team went our separate ways and got all grown up.
Airsoft is very realistic training and it teaches you so much about tactical reloads, battle vision, round count, cover and re-cover each movement, and ballistics of the 6mm plastic "BB"s they fire.