These batteries are rated with 1.6 volt, energy (not capacity) is marked on the cell and is around 2500mWh (The reason for using mWh instead of mAh is probably because the mAh is rather low).
These batteries have been around for some time, but are not very popular, this may have to do with their rather short lifespan in typical AA applications.
They requires a special NiZn charger.
The battery weights around 25 gram.