The mAh is milli ampere hour, a unit of electric charge. Follow the link below for a short explanation:
As for battery life, here are sites that talk about ways to take care of your battery, plus the fact that Li-ion batteries do not suffer from memory effect:
Here's another site that has a different take on memory effect:
Eventually, you have to decide which point of view is correct. Or look for a more credible info source.