What is your maximum capacity in Settings > Battery Health? What processes are running with significant CPU? What's the typical temperature of the laptop according to a stats app? (Temperature is a good proxy for general energy use.)

I'm typing this on an M3 Max; its max battery capacity is 88%. I've got some things running (laptop average temp is 50-55C, fans off), screen is half brightness, and it's projected to go from 90% to 0% in five hours. I don't usually baby it enough to test this, but 8-10 hours should be achievable.