Hello,
I'm working with a tinylily + 0,98 oled i2c display and a cr2032 battery...
When power go below 2.7v the tinylily stop to work but the display have enough power to display...
I remember to have read a line about the ability to change bootloader to have a working microcontroller working with less than 2.7v power batteries.
How to do that sort of work...
Is it a changing fuse values or other way.
Please help.

Regards

Hi- yes it's a fuse value that sets the brown out detection to reset the microcontroller. It's really good to have this in use when on coin cell power- however the next lower setting is 1.8V, which is meant for <=4MHz operation. At 8MHz the 'safe' voltage is ~2.5V, although that's for every part of the microcontroller over the entire temperature range- you may be able to get away with a much lower voltage on a project/prototype.