Don't worry, battery life is independent of the software you run on it...
However, it does depends on how you use the computer.
- Intensively on battery?
- A lot on battery or not?
- When you recharge it?
This is different for some batteries so I guess you could best look up some battery tips on Google,
I always try to connect the power cable a lot because I tend to believe that depleting your battery is bad.
But you shouldn't worry about that,
I don't know the case for a Macbook but most laptops allow you to place a new battery when necessary.
I'm aware that I'll get around 1-2 hours max running Windows on it, but one of my friends (mac maintenance guy) told me that using Windows 7 on macbook pro could damage my battery life permanently, affecting its battery life when using OSX as well.
People can say what they want, I would guess that it could run longer than 2 hours...
But you won't know it for sure until you try it out or have a good frined who has the same situation.