Yeah dont use LR cartos on a slim ecig. LRs are only for bigger battery PVs. Personally I prefer the 3.7V PVs more than the 3.3-3.4V eGo. They give alittle more oomph and provide a great vape. Check out the kGo, E-Power, and Riva. They are all 3.7V PVs and have 510 connections so youll be able to use an array of attys and cartos.
I use an E-power and love it. It uses non-proprietary batteries unlike the kGo/eGo/Rivas and the batteries are 1050mah. I get avg a day to a day and a half on one battery and its very easy to carry a spare bc the batteries are small and if needed, unscrew the switch and pop in a fresh battery and your good to go again. Everything is replaceable on the E-Power too so its cheaper to maintain. I use the 1.7ohm Ressurector cartos on my E-power and it gives a great vape.