>>106467783
Alkaline batteries start at higher voltage and drop off quickly, whereas NiMH batteries start at lower voltage and keep it steady until depleted.
Your clock's voltage cutoff point is somewhere on the purple band in pic related, so alkaline batteries work well until voltage enters that purple band, but once there your clock stops working and you replace perfectly good batteries with new ones, wasting more than half of their charge.
Rechargeable batteries enter the band almost immediately after installation and seemingly never exit it, so your clock limps along in this undead state.
The problem is not the battery type, but the extremely wasteful design of your clock. It is more cost effective to bin the clock than to keep replacing alkaline batteries. A well designed clock works well with rechargeable batteries and even alkalines last much longer than with your current clock.