mAh means, simply put, the amount of flight time you'll get out of that battery pack. Usually the higher the mAh are the heavier it gets. When getting the new ones, pay attention to the Voltage and the SIZE of the battery. I've found out that if you get a larger size one would mean either the battery will be toucning the main motor on the Eagle 50, which I don't think it's a good idea OR you can switch the reciever location with your batter. In any situation you'll have to make sure that the Center of Gravity on your heli will stay the same to get a nice balanced performance.

Andy, (user name YADAC123) has recommended that we should not get a battery larget than a 1500 mAh for the Eagle 50. He is the official Exceed (the company that makes the Eagle 50) representative for this forum.

Hope that helps!