If you use a NiCd rechargeable battery you may ... charge for years. This circuit uses a 10F cap with a switching voltage regulator to increase the voltage from 2.3V to 9V. With a light load ...

The whole circuit is built on top of a battery clip so it can be run straight from the top of a standard 9 volt battery. It’s a circuit you’ll find all over the place, even built into many ...