Tech giant Apple has added an optimised battery charging feature in its Apple Watch running watchOS 9 that will learn from users' charging habits to slow battery ageing.

According to AppleInsider, similar to the iPhone version of the feature, it figures out when it's best to charge the battery to 100 per cent based on the user's charging habits.

Otherwise, the battery would be charged to 100 per cent and then maintained at 100 per cent for the entire time it was in the charger.

The device usually turns on this feature when it detects it has been placed on a charger overnight.

After charging to 80 per cent at full speed, it will be floated until close to when the user picks it up for the first time. Then, it charges at full speed to 100 per cent, according to the report.

Battery health can be extended by minimising the time the battery stays floating at 100 per cent. Since it is not foolproof, this feature does come with a tradeoff.

The battery might not be fully charged, for instance, if the user wakes up earlier than expected, it added.

Users can toggle this feature off in the Settings app on Apple Watch by navigating to Settings, Battery, and then Battery Health. The toggle is at the bottom of the screen.

However, it is not recommended for users to disable this feature.

Instead, users can turn off the optimised battery charging feature when it is actively in use.

Then users will see a message informing them that optimised battery charging is in effect on the Apple Watch, reports AppleInsider.

Simply scroll down and shut it off to ensure that the battery reaches 100 per cent as soon as possible during that charging session.