Ok from what I have found thus far and please correct me if Im wrong... but the only real diff. between the M401, M402 & M403 are the size of the battery offered... from what I have been told or read anyway all the Atomizers and Carts of these series are interchangable... Is it really only a Size thing from lil feller, to average feller to E-Cig on Extenze??? Please if possible explain and details that you may know of these and if any whats the benefit of the smart battery and does it really work???
The "Smart" battery refers to the charge, useful life and behavior, I believe. They charge really fast, at least on the usb charger. About 45 minutes and when they reach charge they stop and the led on the battery tip comes on constant. No further charging is going to happen and there is no point in leaving them on the charger.
They do last well, I get about 7-8 hours of use (moderate user on the M401) and when they are spent, they flash to indicate they need a charge and they cutoff completely. Also pretty well work right up until they are spent instead of just wimpering out.
NO CLEANING CYCLE which is nice. They do have a cutoff if you draw too long, but it seems like that cutoff is generally longer than I'm going to hit on them. Had one battery that cutoff too quickly (faulty) and 3 that do not. Supposed to have a feature that cutsoff if the atomizer is dry. Haven't witnessed or tried to provoke that. Not that interested in cooking my atomizers!!! All in all pretty nice for a mini.