I use them (actually I've gone through, and my old man has,through so many batteries (all but the very very high-end kinds seem to have an extremely high attrition rate. I've just started viewing them as a source of free lithium metal with a high surface area (its essentially a rolled up bi-phasic electrode, with part of it Li metal and part IIRC MnO2, both backed onto a roll, after one part ends, the region of the other material begins without any separation, although its easy enough to tell which is which. And although I have a decent quantity of lab grade Li metal [plus a 100g brick of sodium] there is one rather specialized reaction I much prefer to use lithium mined from batteries for over the lab grade stuff, because it is really, really thin foil and as such as a high surface area, which makes it ideal for the hybrid liquid-gas phase reaction (no NOT the infamous 'shake and bake' meth cook, not that I couldn't perform a birch reaction if I wanted to, indeed I have, for other reasons, and have successfully formed the solvated electron solution with ammonia, although the first few times, simply as an experiment, it being formed and then quenched with alcohol rather than actually used to reduce any sort of substrate. I might be more interested if say, somebody just randomly posted the corresponding norephedrines/norpseudoephedrines) for various more exotic substituted amphetamines through my letterbox, but there are a LOT of ways of skinning an amphetamine-shaped cat), but for one very specific use, that thin foil does come in useful,and e-fag batteries seem to die at a rate enough to provide more than I need for that specific purpose)
I use homemade juice, as far as the diluent goes, its best by FAR to AVOID the use of glycerin/VG altogether, and just to use propylene glycol. Glycerine is prone to dehydration to the enal, prop-2-ene-al, the simplest possible member of the unsaturated aldehydes. Aldehydes generally aren't really things that one wants to be inhaling, enals even less so. Acrolein is truly evil fucking stuff. I won't forget, ever, the first time I made some as a kid, via dehydration of glycerin, although in that case using chemical means to do it, namely heating it with anhydrous sodium bisulfate, distilling off the acrolein as it formed, the stench was AWFUL, and the caustic, choking, lachrymatory (I.e teargas) fumes were even worse. Made the mistake of pouring a tiny bit that ended up not being needed down the sink (don't be too hard on me for that, at the time I was only just starting out in chemistry and was not yet in double figures as far as age goes. And virulent isn't the word. I flushed it with water, and made the mistake of turning the tap (it was a dual function single tap, turn it one way you get cold water, the other you get hot water) with the result that what was left was vaporized and sent back up the pipes like a satanic belch straight from the blackest, foulest pit in all hell, and sending me reeling, clutching my face, coughing and choking and tearing up like crazy.
Acrolein is violently irritant, and most likely carcinogenic, mutagenic and a lot of other nasty -genic things, take your pick, it probably is. World health authority recommendation is a tolerable maximum daily intake of 7.5ug/kg, and in glycerine containing liquids, average yield per puff in 'normal usage' being 10ug. Which IMO is very easily going to equal the kind of use most E-cig users are going to use. This stuff is fucking nasty as hell. Its one of those things that I'll only work with in the lab if there are no alternatives, and if I do need acrolein for anything then I'll be doing whatever it is outside, in full protective gear, elbow-length doubled-up gloves, respirator, goggles, blast shield over my face, thick old leather trenchcoat over the top of an inner, tight fitting zip-up leather, and the gas mask cartridges changed for fresh ones immediately before starting.
There is a way around it, that circumvents entirely the acrolein problem. Use propylene glycol as the sole base liquid. I can't stand the off the shelf liquids, I find its impossible to use them with variable output E-fags because the result is inhaling a cloud of teargas. Same goes for, even more so, when the liquid is almost running out and only a small amount wicks up to the heating element then any glycerin gets pyrolyzed a lot easier when there is so little of it, making for an intensely acrid, unbreathable choking poison gas cloud.
Just use nicotine, flavoring and propylene glycol. Glycerin is a really bad idea in anything that is meant to be heated.
https://en.wikipedia.org/wiki/Acrolein
