Converting HP-25 to NiMH batteries, possible?

[cubytus]

This is the battery holder now. It was cut by its previous owner and there was no spring inside, most probably lost, but no trace of leaks. We can see the glue spot I put to hold the spring in place, as well as the crack on the inner short edge (helps when extracting batteries). Given the wear marks on the holder, likely the previous owner used a hard tool.
   

As for the polarity, I wrote it on the inside, but soon found out it was moulded in the plastic. I'm still a bit puzzled by its awkward positioning. Did HP first design the holder in two parts for disposable batteries, then glued them together around rechargeable ones?
   
   

Interestingly enough, I just tried a different set of NiMH batteries: instead of the Eneloops, I used a set of higher capacity EBLs (2800mAh instead of 1900mAh). Now there are no artefacts flashing on screen, even with the original charger connected, voltage on the battery terminals is 2.65VDC without any AC. With Eneloop, it's 2.9VDC with unstabilized 0.9VAC present.

Granted, I understand NiMH won't last long using such a "dumb" charger, but why would there be such a difference between the Eneloops and the EBLs? Are there diferent kind of NiMH chemistries after all?