2100 mA*h = 2.1 A*h
=>
1.25*2.1 V*A*h = 2.63 W*h = 9,450 W*s [3600 s per h]
I.e., about 9500 joules. This is on par with the Duracell and Energizer results in TFA. I found this encouraging.
This conversion does not take into account the drop in voltage that TFA did take into account, but that the above conversion did not (I assumed 1.25V throughout). But even if it ramped down uniformly from 1.25V to 0V, this would only cut power by a factor of two (and that's very much a worst case).
NiMh cells drop less gradually than alkaline; they tend to be nominally 1.2V for the entire useful lifetime of the cell. Just put a NiMH in an old device with a battery meter and watch it say 80% the whole time...
The Sanyo Eneloops are excellent, particularly for things you don't use often but must depend on them: LED torches, camera flashes & triggers, remotes, etc
This conversion does not take into account the drop in voltage that TFA did take into account, but that the above conversion did not (I assumed 1.25V throughout). But even if it ramped down uniformly from 1.25V to 0V, this would only cut power by a factor of two (and that's very much a worst case).