510 battery life flat out sucks! Nothing more nothing less... However, 510 is my favorite model! That being said, PCC is a MUST, 2-3 Battery rotation is a MUST and finally... When you get sick of the up keep of the battery rotation, a battery mod is a MUST!
Ok, that was a bit dramatic (but not really) and if you are a heavy vaper, those instructions are pretty solid. If not, then you can get some decent milage off of a single battery.
Over all... I find myself swaping batterys as soon I see that lil red light go off on my PCC, ONLY becuase I got caught slippin several times and had a half charged battery and a dead one.... Not very comforting on a night out drinking... It DOES get a bit draining after awhile to stay on battery watch 24/7.
Just my experences, hope this helps!
Oh, I do own a 901 also and you get 2-3x the battery life, however, thats comparing a auto 901 to a manual 510 (not really comparing apples to apples there...)
Chief