Arduino ATmega32u4 low power bootloader

I have a board with the ATmega32U4 MCU that comes preprogrammed with ATMEL bootloader and i want it to be Arduino compatible but in a low power mode (board current consumption <1mA @3V).

PS-The board has the 3x2 pins ISP pads (MOSI, MISO, CLK, RESET, VCC, GND) to connect a programmer. I have an AVR mkII programmer and I intend to use it only one time to lower the consumption. Then I want to use a micro USB connector to change the Arduino sketches.
Hardware I have: ATmega32U4 and it’s 0.1uF capacitors and a 16MHz external ressonator (+ 2x 22pF caps).

I’ve been searching and I know I have to change the fuses to prevent the brown-out-reset (BOR) when the battery is lower than a certain voltage. I’d also have to change the CLK bits to divide the 16MHz crystal into a lower frequency mode to consume less energy.
I found this webpage to change the fuses:
I just don’t know how to do this in Arduino or Avrdude and if by doing this bootloader change the board would still be recognized in the Arduino 1.0 program (boards sections - like a Leonardo variant 8MHz for example).

Does anyone know how to burn the ATmega32u4 board with a low power caterina-leonardo version bootloader, keeping the Arduino compatibility?

Perhaps you want to much. Using a 16MHz crystal and divide it to 8MHz will not work. The crystal itself has to be 8MHz.

Thanks for the answer. But what if i have the possibility to change the external clock to 1MHz or 2MHz? Is it possible to work?

8MHz should work, I don't know if 1MHz or 2MHz can be made compatible with Arduino. It probably can, but needs more work.

That website for the fuses is very good. I use it often.

You can create your own Arduino bootloader: But if you have specific crystal speed or baudrate, you also have to create a new board in the Arduino "boards.txt". I have done that a few times, but it's a while ago.

Did you know about the power versus speed dilemma ? You need a lower speed when running on a lower voltage, that is a fact. But using the lower speed for lower power usage could not reduce the power at all. Suppose the ATmega chip runs full speed, and enters sleep mode. That is very efficient. When on the other hand the ATmega chip is very slow and needs a lot of time for the task, that might be less efficient. It depends on many things, so it is hard to say what is best.

Rule of thumb: in case of batteries, use 8MHz.

Hi again Peter

Well 8MHz might not work with my batteries but i'll give it a try. I opened that website but i don't see the ATmega32u4 in the compatible chips =/. Is it possible to use with that MCU? Yes i understand that reducing the clock won't exactly mean low power. But at least it reduces drastically the atmega current. I understand that i'd also need to use the sleep library because the Arduino runs in the loop wasting power.

Well regarding creating the new board in boards.txt i already tried but it has to match with a desired bootloader (with frequency and BOR settings selected) that i don't have and don't know how to create. Do you recall how to do that?