ok I have 4 phototransistors at the front of my sumo robot, 2 for seeking and 2 for line detection, there are also 3 emitters, before I had all the ground wired up together, but the circuit wasn't efficient and I switched to a better method for range detection, i connected the ground to a MOSFET and my MCU operated the MOSFET so i take one base line reading and compare it to a new illuminated reading, but soldering the GROUND wire to the MOSFET made it so that my sensors didn't have a real ground, and if voltage is too high, my ADC will only tell me 1023, I don't know why it appeared to work with a crappy battery...
I hope I fixed it, I had to clip the wires connecting the sensor to the emitters, and add in another wire for an actual ground connection
I actually have a 3000mAh 7.2V Ni-MH but it wouldn't fit on this robot, I don't wanna buy another small one just to suit this project.