I've never seen anyone who has weighed batteries! Interesting. Any single 18650 battery that claims to be above 3500 mAh, is lying and is junk. Any single emitter LED flashlight that claims more than 900 lumens is also lying. And in reality, that is probably 900 lumens from a bare emitter. In reality, after losses through the lens you probably get more like 750 lumens. I like to purchase batteries online from Mountain Electronics.

budgetlightforum.com is a great resource for flashlights, batteries, chargers, and DIY modding.