Like others said, this is not a great idea.

Unlike most battery powered devices, a spring iron in active use needs real wattage to operate, probably comparable to a small chainsaw or leaf blower. Those also just eat batteries.

The best recommendation is to just use a modern digital iron (see examples mentioned in other post by linker) with a normal ac adapter. Just bring a compatible battery bank, or make a cable for whatever brand of tool batteries you have (18-20V preferred). If you are into RC models of any kind (drones, cars, planes) and that's the reason you need it to be mobile, you have LiPos and you can just use those (xt60 onto a suitable cable).

The only downside is that there's still a cable between the soldering iron and the battery, but honestly it's fine, arguably even better as your iron isn't huge, heavy.