The dotMod dotSquonk (mech) is an excellent squonker. The bottle holds ~10 mls. I have two and one of them is always in rotation. It’s one of my favorite squonkers. It is built very solidly. You won’t ever have to worry about a board frying out. As with any mech mod, it will last for the long haul with proper maintenance.
Also really good… the Psyclone Mods SqEvo DNA 60. Mine is always in rotation. It’s easily my favorite regulated squonker.
As previously mentioned, the Pico Squeeze 2’s are excellent and totally worth hunting down. They are very solid little squonkers. It can take a 21700 battery or an 18650 (w/incl adapter). The Squeeze 2 can be updated to the Arctic Fox firmware which brings its performance to nearly that of any DNA mod. I have a couple Sq2’s.
ETA: The dotMod dotSquonk also takes a 20700 or 18650 (with the included adapter).