Honestly, it depends on quite a few things.
First and foremost is the internal condition of the mechbox. If it's shimmed and greased properly, you'll get a lot more shots than one that isn't.
Second, I'd say the quality of the electrical connections and wiring. Standard small connectors have A LOT of resistance in them. Rewiring to deans or something will reduce the electrical resistance and get you more shots.
Personally, I'm able to play all day off an 8.4v or 9.6v mini battery (1500mah) in a upgraded gun. Some people can't.
"Someone in a Prius tried to race me at a stop sign the other day. I couldn't believe it. I had him for the first 100 feet or so but I can only walk so fast."