It often is. Newer LED flashlights that run off a single alkaline cell always have a boost converter. Electronics that run off 3 cells often have a buck convert

It often is. Newer LED flashlights that run off a single alkaline cell always have a boost converter. Electronics that run off 3 cells often have a buck converter down to 3.3V or a lower voltage, which accomplishes the same thing, often a little more efficiently. Boost converters from single cell alkaline batteries up to useful voltages are usually quite inefficient. If you see something powered by two cells, it might not have a voltage converter because a lot of circuits can operate off that voltage directly. If you use this sleeve inside a device with a built in voltage converter, you waste some energy, and your device gets confused about remaining battery life.