No, it's measured at the battery voltage (which is usually not 1V, and varies with discharge)

It's measured this way so you can most easily estimate runtime by putting an ammeter in series with the battery.

No way. I have no idea how mAh are measured in a lab, but they are certainly not in relation to 1V.

To get Wh, multiply by voltage. 2.6Ah * 1.2V = 3.1Wh. 8Ah * 4V (one cell is my assumption) = 32Wh.

The battery has 10x the capacity of a NiMH (that's the lower limit, it could have two cells but that seems a bit excessive for such a device).

Other than the battery discussion, Nokia devices running RT are about as interesting as the dirt on my shoes.