Low-voltage Christmas tree lights

Battery-powered Christmas tree lights bought at Intermarche for ~$4.
50 white LEDs are connected in parallel, battery holder for 3 AA cells contain also mechanical switch and resistor in series. LEDs seem to be pretty well matched, with no observable differences in emitted light.

When powered from 3 NiMH cells this draws ~60mA. When powered from 2 NiMH cells (one pair of battery contacts shorted) - about 2.5mA, with very low light intensity.
These lamps have nominal parameters specified as 3V/20mA, but it does not make much sense with battery holder for 3 cells.
I have to warn that this one was dead on arrival with cable not soldered to contact. Quality control might be not perfect, but it is still great value if you have soldering iron prepared.
As improvised power source I've used old Nokia charger (ACP-7E) with additional diode and 27Ohm resistor in series.