Actually I’m using 18350s from saberbay in this project.
I’ve watched plenty of tutorials, but was debating the reality of soldering directly to these guys. I could also use battery contacts either soldered on tape wrapped. Basically not-a-chassis set up, with exterior recharge port. For yeas I’ve used wither pre wired cells, or full removable battery set ups. First time trying button cell, chassis free 
I’ve soldered AA rechargeables into electric toothbrushes before. Still going strong after several years.
You’ll just need an iron of fairly high wattage. Those batteries will sink heat quickly, so unless you want to heat up the whole battery (you don’t) you need something with a lot of heating power to make your joint quick and get out.
Understood, thanks for the advice!
I’ll use the widest tip I have, and usually set my old hakko 888d iron to 650f (340c).
I see that people usually do spot weld for batteries.
Or you can buy a spot welding pen for 30usd.
https://www.amazon.com/AWithZ-Handheld-Adjustable-Automatic-Stainless/dp/B0C4NJWM6F/
I did it in my mandolin blaster. I soldered a connector pigtail to a small battery. It did soak up a bunch of heat, but worked fine.
Spot welding… interesting but a bit intimidating. I guess that’s why so many videos are titled ‘soldering to batteries: no welding!’ 
Crank it (my 936 goes to 480c). Get in/get out. Lots of flux.
Scuff up the ends of the battery, turn the iron up high, use some flux to speed it up. The goal is to avoid heating up the battery too much.
Welding is better, but soldering works. Just try to do it fast, or you may ruin the batteries.