Re: ever reaches the density of chemical fuels
Technically Primary cells are chemically fuelled and unless Zinc Air, the "oxidizer" aspect is built in.
There was experimentation of Butane rather than Hydrogen fuel cell for laptops, but then Lithium replaced NiCd. By volume, the NiMH is now about x5 capacity of NiCd and after 100 cycles, perhaps similar volumetric capacity to LiIon, but much heavier. Interestingly if you "turbo charge" NiMH to get them charged in a hour rather than 10 hours and get it wrong, they go on fire too! I know because I've done it developing a turbo charger (the CPU was 486 SoC, replacing the charge control function with an extra 16 pin PIC solved the reliability issue, the 486 SoC was still used for main GUI and Wireless network monitoring features).
Any fuel cell, in theory, can be higher density than a battery always, because it uses air and could vent the water and CO2 produced. I'm not sure that LiPoly and NiMH are not both higher volumetric capacity than current fuel cells. The cost though of "recharging" a laptop fuel canister from butane, I'd think would be higher than mains electricity and Lithium batteries. Maybe a use case in isolated places with no mains?