So, lately I've been looking into (although not as extensively as I might like) the amount of power that batteries found in Fallout actually hold. The only sources I've found for a definitive amount that any portable power cell holds would be the wiki article on http://fallout.wikia.com/wiki/T-51b_power_armor_(Fallout_3) and the article on the New Vegas version of the http://fallout.wikia.com/wiki/Microfusion_cell_(Fallout:_New_Vegas) (which states that it generates power rather than storing it). My question is this, how much power do energy cells and fission batteries hold? Actually, how does power consumption even work in the Fallout universe? It strikes me as odd that laser rifles would consume Microfusion Cells if they're miniaturized fusion reactors (which they apparently are according to the wiki). Is there any actual lore on this at all, other than the seemingly random numbers being assigned to these two specific examples?

Any insight on this would be greatly appreciated!

As far as I am aware the numbers given are just that, random numbers. There is no hard lore on how much power X kind of battery holds really. All we know is that, if left unused, they can last over 200 years.

As for why microfusion cells run out of power, even nuclear reactors need some sort of nuclear material to begin the reaction needed to make energy. Firing a weapon likely drains this nuclear material, and after repeated shots, there isn't enough left to generator adequate power to fire another shot.

Larger fission batteries can be seen powering street lights in NV.

Thanks a lot for the information, it's a shame there aren't any hard logical numbers, but what you've both said is really helpful!