Apple Watch Series 12 vs Galaxy Watch9: health tracking and battery life

Your phone makes this decision before the watches do. The Series 12 needs an iPhone 11 or later running iOS 27, per Apple's tech specs page (checked Nov 1, 2026). The Watch9 works with Android, but its best health tools want a Samsung phone. If you're on a Pixel, read the rest knowing the Watch9 does less for you.

Battery: two tests, not one

No outlet I read ran both watches side by side, so treat this as two separate pieces of evidence.

Apple rates the Series 12 at 24 hours. Macworld measured more than that: 51 hours on its first run and 40 on its second, an average of 45.5 (review dated Oct 6, 2026). Its Series 11 averaged 47.5. So the Series 12 came in slightly below last year's watch and was far less consistent, though both runs beat Apple's rating.

Notebookcheck tested the Watch9 44mm and called its battery the one major shortcoming. With the always-on display, health features and workout detection, it used about 40 to 50 percent between 6 a.m. and 9 p.m. Add overnight sleep tracking and a full day cost 60 to 70 percent (review dated Sept 20, 2026). The cell is 445 mAh.

Charging favors Apple too. Macworld got 58 percent after 30 minutes on one run and 72 percent on the other, with a full charge in 82 and 63 minutes. Notebookcheck says a drained Watch9 needs almost 1.5 hours.

Health tracking

Apple's page lists an ECG app, a Blood Oxygen app, hypertension notifications, sleep apnea notifications and a sleep score. It also lists a Readiness app. Macworld says Readiness needs at least seven nights of wear before it gives a verdict, and that two flagship features weren't ready at launch. Its verdict: "Not bad. But I expected better."

For accuracy, I only have numbers for Samsung. Notebookcheck compared the Watch9 against reference devices:

• Blood oxygen: 0.7 percent average deviation from a Braun oximeter
• Exercise heart rate: 4.3 bpm (1.5 percent) from a Polar H10 chest strap
• Blood pressure: 1.1 percent systolic, 0.4 percent diastolic against a Braun cuff

The blood pressure figure comes with a catch. You need to recalibrate with a cuff at least every four weeks. And ECG, blood pressure and sleep apnea checks require a Samsung phone and the Samsung Health Monitor app. Notebookcheck calls that frustrating for Android users, and I agree. A watch sold as an Android watch shouldn't hold back its sensors from most Android phones.

I didn't find a comparable accuracy test for the Series 12, so I can't say it measures better. Sensors on a wrist are only as good as the data they log.

Size and price

The Series 12 in Products is the 46mm, at 39.5 g. The Watch9 44mm is 34 g. Both are rated for swimming. Apple lists 50 meters under ISO 22810, and Samsung's rating is 5ATM + IP68.

Apple's cheapest Series 12, the 42mm GPS, is $399. The 46mm GPS is $449, per Macworld. Samsung's page listed the 44mm Bluetooth Watch9 at $459.99 on Nov 1, 2026. Comparing the 46mm Apple with the 44mm Samsung, at list Apple is $10.99 cheaper. A translator's note in Notebookcheck's September review put Amazon US's 44mm at about $410. That is a September figure, so check current retailer prices before paying.

What I'd do

• iPhone owner: buy the Series 12, and take the 46mm if you have a big wrist. Charge it nightly and ignore the Readiness hype for now.
• Samsung phone owner: the Watch9 44mm is the sensible pick, and the battery is the cost.
• Other Android: skip both. Browse the smartwatch catalog for something that doesn't lock features to a brand.

Running is where I'd look elsewhere on either side. My best smartwatches for running covers that. For iPhone-only picks, see best smartwatches for iPhone, and the Galaxy Watch9 review goes deeper on the Samsung side. Product pages: Series 12 and Watch9 44mm.