So, I'm building an Arduino toy car. It runs with 4 motors and has 2 color sensors and 8 IR sensors. It must work on battery because i don't want it to be hooked to USB all the time and motors require much more current than USB can provide. So here's the problem...
When I have my arduino powered with USB cable or USB cable and battery, it works perfectly, but when I have it powered only on battery (7.2V), 4 LED's in the left color sensor glow dimmer, and the right one doesn't even work.
I should point out that some of the pins of color sensor that should be plugged in 5V or GND are plugged in digital output pins set on HIGH or LOW.
The arduino i'm working on is Arduino Mega 2560 and color sensors are TCS230.
I think you should measure supply current of the board and then check if your battery is able to provide such value. Also try to feed the board from external supply through wall adapter connector (or Arduino's Vin terminal). The idea is that you may need higher voltage and(or) current, then 7,2V.