I don't believe 1 battery can but say if you got 100 or so maybe you could power a small town or something. I never played fallout 1 or 2 (even though I own them) so I don't really know about the ones they were working on before the war. Care to tell me about them if you have time
There were no such thing as "fission batteries" and new cars cost upward of $300'000 dollars and the rather new Chrysalis "Highwayman" was a car you could get in Fallout 2 which ran on the old-style, car-battery, micro-fusion cells; based off memory that could get you from San Francisco to Reno and back again - off-road; going off Google Maps that's about 600 miles on a full cell.
In the town of Gecko, Ghouls operate a nuclear reactor - at the same site are other, unfinished, reactor buildings which were presumably abandonned because of the war; even the Enclave's Oil Rig had a nuclear reactor and now I remember it a lot of the Vault's had nuclear reactors too. They provide, as evidenced I guess, extremely long-term, high out-put, power generation without the need for having to get more fuel than that stored (Gecko being the exception as it buys Uranium from Broken Hills); I can only assume therefore that these fission batteries are very much similar in intent, designed for consistant, long-term usage - perhaps initially for the military before becoming commercial?