That's pro stuff, way above my league :-) Seriously, my current soldering iron is a dumb piece of crap, I do want to upgrade to one of these eventually: https://pine64.com/product/pinecil-smart-mini-portable-soldering-iron/
I don't think I've ever used (separate) flux; this is what you mean, right? Isn't it supposed to be incorporated inside the solder nowadays?
Good tip, but the OP should be aware that when at 3.7V they have only ~50% charge in them, so remember to also pack a spare or two (at the same voltage) to have the same total runtime.