Remember to use “Charge to Full Now” before going out

On the default settings, modern Macs will only charge to 80% unless you tell them otherwise.

To preserve long-term battery health, modern Macs don’t always charge to 100% when you plug them in. They’ll stop at 80% if they expect to be plugged in for a long time:

Optimised Battery Charging is designed to reduce the wear on your battery and improve its lifespan by reducing the time that your Mac spends fully charged. It uses on-device machine learning to learn your daily charging routine so that it can delay charging past 80% in certain situations, such as when it predicts that your Mac will be connected to power for an extended period of time.

I use my work laptop as a “desktop laptop” – it’s almost always plugged in at my desk, and day trips away from my desk are exceptional. However good the machine learning algorithm is, it can’t know that this particular Tuesday is when I’m leaving the house.

If I know I’m going out, I can explicitly tell my Mac it should charge itself to 100%:

When charging past 80% is delayed by this feature, “Charging On Hold” appears in the battery status menu. If you need your Mac to be charged to 100% sooner, choose “Charge to Full Now” from the menu.

Charging a battery goes faster when it’s mostly empty than when it’s mostly full, so if this is important, it’s worth doing the night before the trip, to get the most out of that extra capacity.

(Quotes from Apple Support doc About Optimised Battery Charging and Charge Limit on Mac )