We're using an Arduino Mega board that has a number of components, but one section in particular seems to be giving us a problem and I suspect that is due to voltage drop when our piezo speaker is activated. Below is a schematic of what's involved. The piezo is a larger piezo and works fine when the batteries are fresh, but the intent of it is for it to be activated later in the lifespan when the batteries have been used for a few hours and the voltage is a little lower - not critically low, but lower. When the piezo is activated it will sound for a few seconds, but then the Arduino shuts off and then powers itself back on - without the piezo on. My guess is a brief drop in voltage. I was thinking that adding a capacitor to this in parallel would solve the problem, but I'm not sure how large of a capacitor to add. The batteries are in series and output 8.4v when fresh and shut off (end of life) at 6.6v. They are 3.7v batteries so the average operating voltage is 7.4v for the pair. During our use, the typical lifespan should see the batteries drop to around 7.2v so we don't usually get all the way to the end of life voltage.