Apple Watch Series 9 Overheating / Rapid Battery Drain in Home Sauna

You are using the watch well outside the recommended environmental parameters. Stop doing that. You may permanently damage the battery and the screen.

Apple Watch Series 9 - Technical Specifications - Apple Support

My feeling is that if you are concerned that the sauna heat may be stressful to your heart, you might want to decrease the time you spend in it. But I'm not your doctor or your parent.

danielwoods282 wrote:

Hi all,

I need some advice on Apple Watch thermal management. Lately, whenever I sit in my tent sauna for 15–20 minutes at around 125°F–130°F, my Apple Watch Series 9 shows the yellow thermometer warning screen and shuts down completely. Once it cools down and boots back up, the battery drops from around 80% to under 20%.

I mainly wear it to keep track of session timers and watch my heart rate response to heat stress, but the thermal cutoffs are making it impossible to log anything accurately. I was troubleshooting my setup against the temperature benchmarks and ambient heat data on this site to see if my setup is just running hotter than normal, but the enclosure temps seem standard.

Is there a recommended way to protect the watch from direct ambient radiant heat, or is leaving the watch outside the thermal environment the only reliable way to prevent battery degradation?

You do not need to use an Apple Watch if you just want to monitor your heart rate in that environment. Conventional chest strap heart monitors cost maybe 10%-20% of an Apple Watch cost. Why risk damaging a device like an Apple Watch? That said, the maximum operating temperature for the Apple Watch is 95 degrees F, so your 125-130 degrees is way out of range, as IdrisSeabright has noted. You have probably already damaged it.

But you will also have a challenge finding any heart rate monitor that will operate at 130 degrees. I randomly looked up some Garmin devices and the ones I looked at specify 105 degrees F as the max operating temperature.

To augment the others' advice please heed the following:

Keep Apple Watch within acceptable operating temperatures - Apple Support

Apple Watch Ultra? Maybe. Other models, absolutely not.

Stop doing that.

👍