Who says they are modern power cells?
They very easily could be 210 year old power cells that have been drained of energy over time, like how batteries and lose power over time even when not in use. And even if they were "modern" they could very easily be inferior due to the fact the post-war makers dont have access to the same level of technology as the pre-war world did. The nuclear war did sort of hamper things in that department.
Why not? the PCs of the older games had access to what amounted to magic powers, via things like mysterious stranger, Scrounger, night vision, animal friend.
And the PC's could do the impossible such as talk down anyone, so long as they had the right speech skill/charisma, and possibly perks.
Why can't the PC be as smart as they are charismatic?