Not sure about the first question but, I have found that if I compile a C PWR_DOWN program outside the Arduino IDE, the result on a bare AVR is sub microAmp. Why does PWR_DOWN still leave the AVRs drawing a few hundred microAmps (deducting LED) in PWR_DOWN? Why are Pro Trinket figures about 0.2mA less than Trinket across the board? In fact, given that nothing is limiting the voltage to the AVR, your consumption will probably go up. Powering via 3V out pin to bypass the regulator is not worth the risk. This example is not particularly demanding. Running consumption will depend on what is running on the AVR. Removing the LED would get to I measured 2.0V drop across the power LED so with the 470ohm resistor you'd save about 2.8mA in all cases by removing it. Note: PWR_DOWN figures for Pro Trinket via 3V output are reversed (transcription error) CurrentDraw.jpg (30.78 KiB) Viewed 2771 times There could be other minor parasitic drains in the circuitry but those two should get you to your target (he says confidently without being prepared to try them himself. If you want to mod the pro trinket, you'll need to desolder or cut the trace to the power led, power it via the 5v output BUT make sure you tape over the USB and FTDI ports or you will forget when you flash a program and end up applying two power sources. So this is a perspective rather than a solution.

Now I expect pwr_down consumption to be less than a micro amp but I don't expect it on a dev board or via the Arduino IDE. That realisation led me to order a USBTiny programmer and learn about programming AVRs without the Arduino IDE. There're lots of threads chasing low power on these boards, but I searched high and low and there really is no 'aha' answer. Heck, I can't even force myself to solder them into projects. I couldn't bear to butcher my trinkets or pro trinkets. If you take off all the pieces that increase consumption on dev boards like regulators, leds, boot loaders, protection diodes etc it's really just a breakout board. Seriously though, while a project lasting a week on battery can certainly be adequate, it's never satisfying when you know it could last for months or even years. Then it's micro amps and before you know it, nothing can fill that burning desire but nano amps. Sure, that's how it starts, you're just trying milliamps.

Adafruit trinket 5v power ma