Our 3-volt lights are for 3-volt batteries only. A 9-volt battery is just too strong and will destroy our 3-volt LEDs. Instead, consider using our 3-volt coin cell holder/switch with a coin cell.
The 9-volt lights are made with a resistor for use on a 9-volt battery or regulated power supply. They will not be bright with 3-volt coin cells. You can use our battery snap with a switch for the 9-volt lights.
If you already have a power supply you use in your project, get our AC/DC lights which have the extra parts to protect for AC power input.