Only the outer two pins are connected in the controller. Very occasionally, the two outer pins on each side of the battery are bridged so that it has two positives and two negatives. The idea is to reduce the current on each pin when you match that on the controller. It's worth checking your battery to see if yours is like that, in which case you could wire something to the next to outside pins on the controller connector.
Also, it looks like you have some fairly meaty red and black wires running down the length of the controller. That's probably a branch off the battery wires for the LCD. You could scrape a bit of insulation off to check with a voltmeter then splice your wires there.
I still think that a separate 12v power-packed would be a better solution.