I have owned both Smok V8 and Smok stick22. The 22 can't be fixed as far as battery replacement and internal 510 pin issues. The Smok V8 CAN BE. Try this carefully:
Unplug charger from mod. With a tank on tight as if you were going to bust a stick in half, with tank in one closed fist and the mod portion in the other closed fist. Slowly wiggle while pulling, and watch the gap between the mod tube and the top 510 female fitting. It will SLOWLY wiggle apart, and you'll start to see splines appearing in the seam where tube and top fittings meet. Wiggle slowly, and the top, with the electronic chip and battery will slide out with it.
Now, carefully clean internal parts with a damp paper towel. Clean all oil off of inside of tube. If your button is loose, put a tiny dab of super glue on sticky side of the tape that holds button in place, and then hold tape back onto inside of tube for 10 seconds.
Next, for 510 issues, take a bright light and look in between the button and the metal portion of electronics. If you push in the spring loaded pin via the top of the 510 connector, you'll see that pin is pushed in, it touches another tiny pin in center of chip. You'll see this if you look into gap. The pin attached to chip is the issue with the sticks 510 connection. If you can, use a qtip and soak up any liquid. Use a toothpick (nothing metal) to push chip pin around, and attach tank with coil and juice to see if it fires. Make sure all surfaces of connection - from coils bottom grommet to the 510 male and female are totally liquid free. Gently move pin on chip until stick fires. PATIENCE and BE GENTLE.
FINALLY, you see now that a battery replacement can be made. All you need is a solder iron and some good solder.
Place a 2” piece of electrical tape on top of battery between battery and chip and secure piece down sides of the battery before re-assembling mod.
Slowly line up tube and top piece making sure that the charge port and plug on charger meet with no hang up on tube.
If you don't have patience or the proper tools, take it to the vape shop APART and have them fix it.
You can learn this process, replace Smok stick every time it fails, or get a better mod, and I personally suggest the Smok Procolor “Mod Only" since you can use your V8 tank and coils from the 8 stick on the Procolor and save a few bucks for some Vaporesso coils.
OTHER TIPS:
Change coils as slow as possible, and don't remove entire tank to do so. Remove top of tank while holding stick upside down, and then use dropper to empty. KEEP vent piece on since taking it off will aggrevate 510 issue or create one.
Allow juice to soak for 10mins and make sure to SHAKE UP JUICE before you use it if it's been sitting any longer than a day, and to keep clean, use low sugar juice.
These are the issues and repair options for the Smok Stick V8.
Patience, precision, and good luck enjoying the V8.