After my initial consternation about the temperature control costing $170, I think I have an idea that may placate my concerns.

A compact temperature control widget without batteries at all.

It accepts the appropriate USB PD power input in a standards-compliant way. It has a knob, and also a screen for status. It talks to the soldering iron and provides power to it. It does not have batteries or any special facilities for batteries *though if a user chooses to use it with an appropriate USB PD battery then they certainly can). This all seems possible, and adherence to USB PD specifications should tend to make it safe by default.

The rub, and this may not be possible at all, is that it must be substantially cheaper than soldering iron itself.

But because you've done the right thing and documented the protocol, then maybe someone else will implement this (as DIY or otherwise) and it won't be your problem at all. :)

Out of curiosity - why not offer tool battery adapters, e.g. DeWalt/Makita/Milwaukee/Bosch (depending which color you bleed). Those are ubiquitous 18v - have fast charging, and drawing 100W is fine even for the 1P types, e.g 2Ah. As a bonus they have excellent mechanical properties (usually PA6 or PC/ABC bodies - so even dropping the soldering iron on them would be okay)

Of course, a pack of 6x MJ1 is relatively trial to built (except it'd require some decent plastic body)- esp for 2s/3p, still not very useful aside running that particular iron/tool (and most likely end up charging it w/ the power supply...)

Sorry to hear that, and good luck. Additionally I apologize for the undue cynicism, but as a flashlight enthusiast I've been frustrated with this problem for years and years. The form factor of a battery charger and USB powerbrick/supply would be so nice! It's massively annoying to me that I own many 18650s and still need to buy and replace power banks.

Worse, it seems like the manufacturers best suited to make the product I desire(anker and nitecore) are directly incentivized by obsolescence to not ever make it. The best thing I've found so far is the Nitecore LC10, but it was discontinued. :(

I sort of suspected that it might be the case of safety bodies getting in the way. I really hope you make progress with UL. I'm rooting for you. There should be a way of overcoming this problem.