Apple Watch Series 8 - how to extend battery life for my Outdoor Cycle rides ?

Hello. I have an Apple Watch query. When I go out for an Outdoor Cycle using Apple's Workout app on my Watch Series 8 (GPS) and Watch OS 10.6.1 the battery lasts about 8 hours until I get a low power alert.

I would like to monitor my heart rate so permanent Low Power mode is not an option.

What do you suggest to extend the battery life for my rides?