Do eneloop batteries (1.2V) in comparison with alkaline batteries (1.5V) work in every battery based appliance?

In general, appliances are designed to match the characteristics of dry batteries and to work within the voltage range of 1.5V to 0.9V.
Although the initial voltage of Ni-MH rechargeable batteries is around 1.2V, which is lower than that of an alkaline battery, they are capable of maintaining a steady discharge level at around 1.0V for as long as they hold capacity, while alkaline batteries constantly decrease their output voltage from the moment they are in use. 

Thanks to this characteristic, Ni-MH rechargeable batteries can be used in appliances which require alkaline batteries, even with lower initial voltage.