The Apple Watch Optimized Battery Charging feature uses on-device machine learning to discover your charging habits over time along with your daily usage to either charge the Watch to an optimized level or charge it to full in order to improve the lifespan of your Watch battery.

This will slow down the wear on your Watch battery to improve its lifespan by reducing the time your Apple Watch spends fully charged. When turned on, your watch delays charging past 80% in certain situations, so that the battery level remains between 75-80%. Optimised Battery Charging is only activated when your watch predicts it will be connected to a charger for an extended period of time, and still aims to ensure your Apple Watch is fully charged when removed from the charger.

If, for example, you mostly leave your Watch on charge overnight, Optimised Battery Charging will slow down the charging to make it more efficient over the period you are usually asleep, while still making sure that the battery is full and ready for your daytime usage by the time you wake up.

When you can't get to your Apple Watch charger fast enough and the Watch battery is dangerously low, you can eke out the remaining battery charge by saving power.

The easiest way save battery life is to turn on Low Power Mode. This turns off Always On Display, background heart rate and blood oxygen measurements, plus heart rate notifications. Cellular access is also turned off in Low Power Mode. If you're just going for a walk, then maybe you don't need the heart monitor on—although this may impact your Exercise score, it could keep your Watch going till you get back to base and a charging socket.

To turn on Low Power Mode, tap the side button on your Apple Watch to open Control Center, and select the battery percentage. Then tap Low Power Mode.

Apple states that "other notifications may be delayed, emergency alerts may not arrive, and certain cellular and Wi-Fi connections are limited" in Low Power Mode.

When the Watch battery is charged to 80%, Low Power Mode turns off automatically.

Other Apple Watch battery saving tips include:

See: How to improve Apple Watch battery life for more advice.

The Apple Watch battery life is notoriously short between charges so fast charging is a great way to keep your smart timepiece topped up and ready for action.

Using a Fast Charger cable, you'll get fully powered up in the shortest time so look for Watch chargers that support fast-charging.

An eight-minute charge should power your Watch for eight hours of sleep tracking.

Fast charging requires at least a 20W USB-C charger.

See How to fast charge Apple Watch for more information.