I would not want multiple cells for reasons of ergonomics and convenience.
I probably don't need 100W for most field soldering. 60 is plenty, and temperature-controlled soldering irons usually don't need to pull high current continuously. It would need 60W for maybe 10 seconds when powered on, and when heating something large. The rest of the time, it takes relatively little power to keep the tip hot.
What I'm describing is, of course not the right tool for production soldering. It's for field work.
I've got a Ts80p which is a qc3 usbc soldering iron for that. It's crazy powerful for it's size and runs off a pretty small anker powerbank. You could slide that into your sleeve to go portable and one handed
Having used a butane iron before, I don't think it would. They don't have the temperature control modern digital irons can, and they're forbidden on flights.
I haven't done the math, how much runtime could you get out of a single 18650? They're pretty stout, but it seems like they'd be a bit underpowered.
Milwaukee 12v batteries are 3 cells (I think they're a little smaller than 18650), and you can run through a battery pretty quick (I believe they're 1.5AH). Though I don't know how efficient their heating design is.
Assuming the M12 CP1.5 battery pack, it's probably three 18650s. Specifically, it's probably three LG HB series 18650s, which handle high burst loads well, but hold only 1500 mAh. A single Sony VTC6 holds 2/3 the energy of one of those packs. Wait... why am I speculating? Youtubers tear down power tool battery packs on video all the time, and someone did that one. They're Samsung 15Ms, which are a little worse than HBs.
Anyway, short runtimes are fine for most field repairs, which is the whole point of something entirely self-contained. Spare batteries can extend it indefinitely, but a battery soldering iron is probably not what I'd pick for extended soldering sessions.
Lol, I get it, I often start doing the math and realize "someone has already done this".
Cool, thanks for the link. I already knew the little 12v batteries suck (though they work fine for the intended purpose, like impact driver or work light). I kill them with any other tool.
Yea, I was just thinking is the runtime reasonable enough that having spare batteries is a sufficient approach. Like you said, long runtime isn't required, 15 minutes total runtime is probably more than enough (though that would be hell on battery life cycle).
Since I already have a slew of Milwaukee batteries, I'm trying to avoid things with 18650, except where form factor matters (like my flashlights). A Single Battery to Rule Them All (or at least most things).