[xxs]

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...)