Great runtime.
The meters will not be accurate unless there is a setting for this battery type on the recorder. But with that much time you may never need to rely on the battery indicator anyway.
Alkaline batteries are 1.5v nominal, NiMH are 1.2v, these are 1.6v. In addition, each battery chemistry has different voltage discharge curves. Generally, standard cells taper off more evenly and more advanced types keep the voltage up for longer, but then voltage drops off rapidly.
Not sure how the Sony's batteries are wired, but either 2 or all 4 cells are in series, multiplying the voltage of each cell. That means when using NiMH batteries the recorder 'sees' either 2.4 or 4.8v, with alkaline cells it 'sees' 3 or 6v, and with these batteries the recorder 'sees' either 3.2 or 6.4v.