This problem occurred recently. I cannot use 2 rechargeable batteries but only 1 rechargeable batteries and 1 normal alkaline battery. I checked both of my batteries and they only work in that way.

Rechargeable batteries provide .2 V less than regular batteries (say 1.3V vs 1.5V). So, with two batteries, that’s about .4 V and if the batteries get old, maybe more, which explains why your device does not work.
The extra battery provides the extra voltage you need.

But new ones.