"Another problem is efficiency. At 1 amp, the DC-DC converter is about 75% efficient, and is only 65% efficient at 2 amps. I have not tested the converter’s efficiency at lower loads yet, but I doubt it will achieve more than 85-90% efficiency."

This is why, and it's an unavoidable problem with making 3.7 volt cells work in devices designed around 1.5 volt alkaline batteries. They still have the useful advantages of lighter weight, faster charging and apparently greater voltage stability.

18650s do not have this problem as they are used in devices designed around their native voltage.