It uses a standard 3V CR1220 battery in order to blink 12 LEDs. The micro-controller is an ATTiny85-20MU that drives directly the LED’s. The first iteration used 3 AG1 batteries but I switched to the more covenant CR1220.
I need a voltage over 2.2V in order to light the LED’s but I don’t power on all LED’s at once, so I don’t need a driver for them. I can easily get 20mA from the digital pins of the ATTiny85.
Check the working video: