Anshity, whatever you are using, it is either negative ground(common) or pos ground. Kung negative ground, it means yung output line from an port is positive di ba? I don't know how many LEDs can each port handle. Parallel lang sila dapat after you have confirmed na ang output V is match to the LED V you have. if you want extra load, then first , you need to use a bigger battery of the same V. Even a power supply or nicads. Gamitin mo ng NPN transistor such as the C1062 or look up the Alexan product catalogue which pone is the NPN dun sa TIP transistors. Her is the connection:
YUNG OUTPUT NG PORT, SERIES MO NG IK RESISTOR AND CONNECT TO THE BASE OF THE TRANSISTOR.
YUNG EMITTER NG TRANSISTOR GROUND.
YUNG COLLECTOR SA LEDS NAKAPARALLEL.
YUNG KABILANG TERMINALS NG MGA LEDS SA PLUS LINE.
K TO USE A SEPARATE BATTERY TO THE LEDS DUN SA 9V MO SA GAMIT SA IC.