The good news is that the Forerunner 965's switch to AMOLED hasn't resulted in a reduction in battery life.

However, if you're looking for a watch that can withstand a week of tracking and use of its smartwatch features, 

this is what you can buy. There are minor decreases in specific instances.

According to Garmin, using the screen in always-on mode can extend battery life by up to seven days while using the GPS up to 31 hours. 

When similar always-on features are enabled, you'll receive longer battery life

from that device than from an Apple Watch or Samsung Galaxy Watch.

 Battery life for the Garmin Forerunner 965