I'd check what color they emit as well.
Red usually has a voltage drop of 1.6-2.2 volts, green and blue 3.0-3.6 volts and white also 3.0-3.6 volts.
3.7 volts will work for a lot of leds, but isn't a standard value....
Leds with an aluminum plate for heat-excange usually are 1 watt or more. Without they're often using less then 1 watt.
Do you have any pictures of the leds ?