Sometimes my coils just get loose, and nothing, no vapor even though the battery appears to be fine.
Take off the mouthpiece, and make sure the coil is screwed in snug.
1. This is the most common problem...it's essentially a T2 clearo and sometimes the replaceable head assembly gets loose.
2. The next problem with 808 style batts is the center post on the battery gets puched down a bit...nudge it up a just little with a paper clip or tweezers.
3. If the battery post gets too much moisture, it could short.
4. Once I had some lint in the battery post area...ya never know.
If you have another device, try it...then you'll know if it's the battery ot the tank.