Forward voltage drop across the LED is 2.0-2.2V, so I decided to connect them in parallel, and to use step-down DC-DC, which converts 3.0-4.5V from 3xAA to 2.0V.
Details
In action:
Schematic:
PCB layout:
Final PCB:
Macro-shot:
Components
50×
Candle Flicker LED
1×
ST1S10 step-down DC-DC converter
Power Management ICs / Linear Voltage Regulators and LDOs