Can I replace my battery with another one that has more mAh?

I have the first macbook unibody made in 2008 (model a1278). It's been almost 5 years since I've had it and I think it's time for a new battery. The battery health is around 55%. So the charge is half gone. It lasts about an hour instead of the 3 hour charge. I don't want to go back to 3 hours, but I want it close to the new MacBooks that hold around 7 hours. Is there a battery out there that I can put in this macbook that will last longer than 3 hours? A friend said to get one with more mAh, but I wanted to ask iFixit for help first.