I have heard this talked about but never done it myself, I'm sure there is something I maybe just don't understand
but to me the chargers cut off at 4.2v and these batteries hold voltage pretty good, so I don't see what the benefit is leaving them charging
if they are
not charging
I know phone batteries when show full normally have to be left for a while for the trickle charge to finish, but I thought that was down to the way the phone works out the battery level (not too accurate)
But they don't actually cut completely off you see. They still keep a small current going (or try to) to do two functions, 'find' a battery to charge and to 'unlock' protected batteries. The first time up, the battery (really a 'cell' technically since there's only one unit) the cell 'forms' as the chemicals inside 'charge'. Normally two reactions happen, one at each plate, with one 'side' favored with enough extra that the other limits the charge by running out first. I forget which in our case, but it doesn't matter.
So to charge we apply a limited current, in the case of Air it's about 700 or 800mA. It slowly rises in fact as the charge progresses. When the voltage reaches 4.2 or so the charger switches to 'constant voltage (rather than constant current) mode pushing whatever current is possible without going too high in Voltage. This current drops slowly as the last 10% or so of the capacity is charged. When the current drops below another threshold (typically 10% of maximum), charge is cut off. It's not complete but nearly so.
Forming charge allows for the 'last' of the material to convert, either by slow trickle from the search current or by 'hickups' of short recharging. In small cells (like the tiny 350mAh Ego 'battery' I was messing with the other day) this can go on many hours. The first discharge forever cuts this 'sweeping up the residual' and that remaining material never joins the game.
Or so it was explained to me many years back. Battery University has some stuff on the subject as do the various specification sheets for charger ICs. You'll find this advice in some but not all vape instructions (even though they use the same batteries). One has to wonder why......some might think some makers don't care? Others would be happy to sell you a replacement, provided the original makes it through warranty. Also tied up there is, of course, decisions about what level (voltage wise) to limit charging to and what discharge voltage they will allow (both of which also effect battery lifespan). There the urge is, naturally to push it, since 'lots of sessions per charge' sells.
Aren't you glad you asked?
OF
I get, although after checking capacity on all my cells they all fall within range, but a little extra is always nice.
