All of today's rechargeable batteries for portable devices of all types are this way, even notebooks (laptops), cell phones & cordless razors, never run them dead. It's a surefire way to killing the batteries.
I've see many who took their cell phones & destroyed the batteries in months, would run them dead, plug in for 30 minutes just to be able to talk for 5-10 at most & start over again. Same with notebooks. Pay attention to these, when there's roughly 40% remaining, put it on charge.
And the same with mod batteries. It's best to know what your battery operating range is & have a less than $10 multimeter to test the batteries, even ego devices can be tested. Just set the meter to 20VDC & check it. The average operating range is from 4.2V down to 3.7, when they drop below 3.7, even if still hitting, place on charge.
That way, the batteries will last much longer & save one money in the long haul.
Disregard any advise telling someone to let the batteries to run down until no longer working, one who sells them may say to do this because they'll soon be coming back for new ones. Also, never take a battery directly off charge & begin to use, as this will surely kill them. Same when using, if one's been chain vaping & the battery gets weak, let the battery sit for 20-30 minutes before charging.
It's OK in an emergency to go down lower, but not on a regular basis.
Cat