It seems mainly for environmental reasons the NiCad cell is now only used for military and medical applications and we now have no option but to use NiMH cell. With pre-built batteries as used in drill etc. there is no problem. But were AA cells for example are used there seems to be two major problems.
1) Suitability of battery chargers. The Delta Voltage chargers need to be far more precise for NiMH so although where the 16 hour charger is used there is no real problem the old delta voltage type (Fast Chargers) can cause the new NiMH type cell to explode. As a result in the main fast chargers don't charge cells as a battery but as single cells.
2) The mAH for a AA cell varies from 600mAH to 3100mAH a massive 5 times and clearly the mAH ratings should not be mixed either with charging or using.
With items where the battery is charged out of the appliance there is not real problem it just takes some care and with me two pair of glasses to see the details on the cell.
But with existing equipment needing the battery changing there is more of a problem. Philips, Panasonic and Binatone phones all use AA or AAA cells. The Binatone MD6200 although still sold is getting old and the Binatone site has no info. The same applies to re-batteries radios just fitted a set of 8 NiMH in my FT290R this is a really old radio at 60ma I would not think a problem, but the point is how do we find out what bits of equipment can and what can't have the NiCad's replaced with NiMH?