It may be time for a mini lesson on MAH -- As I understand it, the length of a time a battery lasts is mainly a matter of MAH, how much you use it and how old the battery is. New Ego Style 650 MAH do last about 5 hours, fairly heavy use.
So, I can't tell if you've got "fat bats" or "long skinny bats" or "something in the middle". Some of the "fat bats" are 900 & 1000 MAH--and are, of course, longer physically as well as fat.
Now, a lot of the mods use 18650 batteries (that is a size description, not MAH or anything else) You can get them up to 3000 MAH, tho I think most have been quite happy with less MAH. 1450's can be purchased at various MAH levels as well.
As you look for MODs pay attention to what you Like about your current system and make sure you get something that delivers that aspect....and, as many Box MODS use 510 threading, you are partially there already. If the biggest problem is time on battery, go up a size with your current system (it's always good to have spares) while you check out some of the pretty exciting MODs coming out this year & save up some bucks.........just my opinion --- I'm pretty new, too --and learning fast!