Use the Simple face 'striped' down/no Complications and in pure green or red (blue is a larger sub-pixel) to save the most power. The more black the less power. As
exxxviii points out pure white is the most power hungry since all 3 sub pixels must be driven. Monochrome will use the most power and red or green using the least. Also bigness needs to be a minimum you can tolerate.
Me, I would just rather charge it and use it.