Samsung Galaxy Watch 9

The Watch 9's platform is efficient, but the defaults assume you want every sensor running continuously. Two changes roughly double real-world endurance.

The two that matter

1. Continuous heart-rate and stress tracking. In Samsung Health, switch these from continuous to periodic (every 10 minutes). Unless you have a specific medical reason to watch for events in real time, the periodic reading is enough for trends and workouts.
2. Always-On Display. Turning AOD off is the single biggest saving — the screen is the largest draw on any smartwatch.

Also worth doing

• Trim the always-listening voice assistant if you don't use it from the wrist.
• Drop background app refresh for anything that isn't fitness or notifications.

The rule

Periodic sensing plus AOD off takes the Watch 9 comfortably past four days between charges, with no loss of the data most people actually look at.