Daniel, here are the possible locations for hooking up extra LEDs:
With fresh batteries (1.55V each) there is 3.00V available across the blue and red pads. The 0.55V is dropped across the the chip which turns the lights on and off.
The white LEDs on the board are hooked up in parallel pairs, then with a 100 ohm resistor in series with each parallel pair of LEDs. Ther Vf of the LEDs is around 2.7V and each LED consumes about 1.5mA (yes, very low current).
If you hook up external
white LEDs I recommend using a 220 ohm resistor in series with each LED. For red LEDs, which have Vf of only 2V (which are also less efficient than white LEDs) a 220 ohm series resistor will set the current to about 4.5mA which should be bright enough. Or if that is too bright, use a 330 ohm resistor, or higher with the red LED.
Remember, these batteries have a very small storage capacity - every LED added to the circuit will reduce the battery life. As-designed, all 6 LEDs only consume a total of 9mA of current on a fresh battery, and less as the voltage starts dropping.
