>>296049608
Anything that takes alkalines but struggles with NiMH would basically be giving out on the alks while they still have over half their power left. So really bad power design.
Alkalines run all the way down to less than 1V before they're considered dead and they voltage sag hard under load. NiMHs on the other hand sit around 1.2V for like 90% of their discharge and sag a lot less under load so their output is way more stable.