i think Mr. Bert's zener regulator is better option
not for battery operated equipment. A zener regulator increses power consumption.

The idea of a diode in series is fine with one exception: the thang will quit when the battery start going low. If the battery chosen is so that it run full voltage and suddenly drop to unusable, then fine, I just do not know any such battery. Using a buck-boost switcher is the way to such every little drop of energy out of a battery.

Erik