Just my

, so take it for what it is worth:
Not sure there is anything wrong with your Kaos. Trying to fire 120 watts on any dual 18650 mod, especially with questionable
batteries, may not work well or be worth the risk. I don't do a lot of 120 watt
vaping, but if I do on a dual 18650 mod, I only use it when the batteries are fully charged. Then I stop when they get even close to 50%. And if it helps, you can shorten the screen time and/or turn off the LED's on the Kaos.
To eliminate any problems, I bought a married a pair of Sony VTC5A 25a batteries. But since battery life was shortened, I got a quad 18650 mod and a set of 4 married 30Q batteries. That will run at 120+ watts much longer then I need and would guess it would last the day if one wants.
Lastly, only get batteries listed and from verified vendors on the chart Eskie posted on page one. No exceptions! Then invest in a decent external charger, preferably a 4 bay in the event you ever decide to go with a quad battery mod.
Yes, all that will cost north of $100, but a good start would be the charger and a pair of the Sony VTC5A for less then $50 which may satisfy your needs for now.