I have an 8-cell NiMH battery pack (10V) connected to a UBEC voltage regulator, so that it provides a constant 5V as the batteries discharge. This is wired to the micro-USB connector that's connected to the Pi.
The voltage at the end of the USB connector is 5V, but the voltage at the test points on the Pi itself is only around 4V. The pPi turns on but won't activate the webcam or the wireless, and soon gets a kernel panic. What's causing this drop in voltage, and why do they even differ? I thought the test points were wired directly to the input connector?
The problem turned out to be the cable - the resistance of the micro usb connector that goes into the pi was 2 Ohms