First & foremost, I have had a few drinks tonight + I'm not up on recent batteries. I checked out moochs post on battery ratings & didn't see anything on watt hour. I'm confused on watt hour ratings. Higher is better, right? I'm currently using hohm life 18650. In my triade, I'd go to bed on a normal day at roughly 50%. So if I switch to the odin running 21700, what can I expect if I upgrade to that size & not run the sleeves for 18650?
The Wh numbers that Mooch lists are in his battery test results. On his personal blog there's a link to all his battery tests, like he explained in this video:
The Wh number is accurately representative of the vaping time you'll get so, yes. Granted, the efficiency of the board inside a regulated mod can skew results, but DNA boards are known to have great efficiency. Aside from that, there can also be slight variations in the vaping time depending on things like the duration of your puffs and how long you wait between puffs, and the temperature of the battery. But these differences are no bigger than a few percent. The only factor that
does significantly affect the Wh number is the number of amps that you draw from the battery. The further you stay below the true CDR ("true" = as reported by Mooch in his test results) of a given battery, the more efficiently the battery runs. So at 5A per battery the 50E2 gives 13.7Wh, which is better than the P42A. Whereas at 10A per battery the 50E2 gives only 12.2Wh versus 12.4Wh for the P42A making the latter battery a slightly better choice in pure terms of the vaping time you'll get from a regulated mod.
In any event, staying at or below the true CDR of the battery that you choose is what's always recommended, when it comes to battery safety limitations. A quick 'n easy way to convert watts to amps for regulated mods is to divide the watts by 3, and then divide that by the number of batteries that the mod uses.
EDIT: If, for how you vape, the difference in Wh between two different batteries to choose between turns out to be rather subtle, then I suggest going for the battery that has the higher CDR of the two.