There are suppliers of individual cells to replace those similar to installed
ones within the official battery housings; portable Macs, PCs; and air-hats.
Shops perform battery replacement on the air-hat types of things; those
with face screen, a reverse air-flow, and a filter behind the poly helmet.
Have a battery on the user's belt. Battery runtime varies from 3 to 6 hrs.
A shop with knowledgable 'skilled soldering person' can assemble one.
A commercial product, while the batteries are similar to those in portable
Macs & PC computers; those don't have as smart of a charging technology.
(Yet the 'smart part' is a circuit & shares space inside the Mac battery case.)
However older iPowerBook G3/G4 whose batteries often held together
with screws + glue, should be easier to replace kit than only-glued ones.
Those powered filtered electric breathing apparatus used by craftsmen
to filter hazardous particulates, while they do intricate work. These see
repair service through their retail sales; as do other electronic repair.
[A buddy makes IRBI custom knives (+ hands-on crafts) has two air-hats.]
Perhaps an external rechargable kit can be adapted, as workaround.