I don't know. This is just anecdotal but I just brought my 510 to a picnic last weekend (regular not mega battery) because I didn't know a lot of people and didn't want to whip out my 1000 mah battery with the EMDCCs. I only had LR cartos which I know is a no-no but used them anyway. I didn't chain vape every second, but I vaped a lot plus everyone of course wanted to try it. And my battery with the LR carto lasted most of the day. I think I might have put a new battery on toward the end of the day. I didn't time it or anything but it was a heck of a lot longer than 1-2 hours. Plus my batteries are about 3 months old, plus I was using LR cartos.
With brand new mega batteries, SR atty I would think you'd get longer than that.
Unless I got super duper batteries!
Maybe it's the charger?