Indeed Blue that is exactly what I meant with my comments concerning of deep cycling vs shortened longevity vs cost. To discuss this properly one has to take into account a few variables like rate of discharge, state of charge, and battery chemistry. E-cig manufacturers are known to be a little vague and misleading with their claims. Ever heard that a 1 ml Cartomizer is equal to 1 pack of cigarettes? How many of you believe that statement? Do you believe every battery will really get exactly 300 cycles, no more, no less?
If you wanted to get the absolute greatest amount of cycles from your Li-on battery then you should do the following. Only use them while you are standing in a 34F degree meat locker and never remove them from the meat locker. If fully charged voltage is 4.2v, recalibrate your charger to only charge up to 4.1v then check the battery and recharge it at 3.8v.
Of course, going to such extremes for battery longevity is a bit overkill. In the world of Li-on batteries what is this mystery number that is considered fully discharged? Is it 0? Well the accepted fully discharged voltage is 3.0v for a 3.7v battery. A fully charged battery is considered 4.2v, but we know from Professor Morandir (or is Dr.?) that the fully charged number can vary from device to device but hovers around 4.16v - 4.2v.
If you have ever read any back and forth between the Professor and I discussing battery voltage testing results we note how many minutes it takes to get from 4.2-4.1Xv to around 3.85v before drop off or battery fade occurs. If there is sweet spot in vaping juices, this voltage range is the sweet spot for 3.7v unregulated Li-on batteries for vaping.
Ideally you want to avoid deep-cycling, but how does that translate into numbers? The State of Charge is 0% when fully discharged or in this case an accepted 3.0v and 100% fully charged is 4.2v., we have a range of 1.2v. Testing shows us that to attain maximum battery longevity it is best to not drain the battery past 40% of the 1.2v State of Charge or 3.72v. From the good Professor's testing we know that blinky blinky time occurs around 3.65v +/-.
Experienced Vapers usually can detect battery fade as flavor and vapor start to fall off especially when using a standard 1 ml single coil cartomizer. However battery fade can be very hard to detect for new Vapers, when using strong flavors, or using a dual coil set-up with a battery that has quick drop-off. A quick drop-off being that time from 3.8v down to 3.65v blinky blinky time.
Now most Vapers usually have multiple batteries and use them in rotation with an average 1 charge every 1-2 days. At 300 charges we are looking at 10 months to 15 months of use. Of course we all know that may vary but it's my experience not by much.
When folks chime in and say, "I have only had my battery for 2-3 months and it's dead, what's the deal?". The first question to ask is, "How many batteries do you use and do you always use the battery until it blinks?" If they only have 1 battery and charge it 3 times a day, using it until it blinks each time, that battery has a shortened lifespan and is simply all used up.
There are other factors that can have a dramatic affect on battery longevity like temperature exposure. Person A lives in a cool climate and always vapes until blinky blinky time. Person B lives in a very hot climate (Death Valley) and works outdoors all day long. They keep their batteries in their pocket or in their hot truck throughout the day, but stop using their batteries the second the detect battery fade never waiting for blinky blinky time.
Who's battery will have longer lifespan? Person A will have a longer lasting battery due to the affects of temperature exposure and the slower rate of battery discharge despite their deep cycling tendencies.
Personally I try not to wait for blinky blinky time, but it happens and I really don't give it much thought. If I can get 230 cycles or a year"s worth of use out of my $15-$20.00 battery I can live with that. Especially since $15-$20.00 worth of analogs would last me about 3 days. The 3 worst things you can do to a Li-on battery is to deep cycle, over charge, or expose it to high temperature. So you would never want to advise any Li-on Battery user to deep cycle their batteries, deep cycling is primarily for older Ni-Cad batteries due to the different chemistry involved.
Is it some giant conspiracy that the battery manufacturers set the cut-offs around 3.65v to shorten battery lifespan? No. All things in the world of electronics have a variable factor. Take a 100 batteries and you will find fully charged ranges varying from 4.2v to 4.1Xv. The manufacturers simply took the low number like 4.15v, giving a State of Charge range of 1.15v, 40% of the State of Charge is .46v, which places a cut-off of 3.69v. Ideally a 4.2v battery would have a cut-off of 3.72v......anything less than that is technically deep cycling.
If you can avoid blinky blinky time, than do it. But if on occasion you can't (happens) it won't shorten the life of the battery instantly, although if you deep cycle every time it will indeed shorten the lifespan of your battery. The big question which only you can answer is.....is that shortened lifespan vs cost acceptable.
When I smoked I never smoked a ciggie all the way down to the filter. I generally put them out leaving about a 1/5 left, so that 1/5 or 20% was an acceptable loss factor for me.
Morandir has some cool test results from Blinky Blinky vs No Blinky Blinky...and total charge cycles.