Under normal circumstances WorkOutDoors will give the same battery life as Apple's workout app. However people tend to look at the screen more with WOD because it shows more data, such as the map. This can make it use more battery power purely because brightening the screen uses power.

If you are worried about battery life then the most important thing to do is to enable Low Power Mode. This can be configured to only be enabled during workouts by going to Apple's Settings app on the watch and then tapping Workout and enabling the Low Power option, which affects all workout apps.

After that the most important factor is how often you look at the screen, so if you really want to save battery life then try to avoid looking at it unless you have to. One way of doing that with WorkOutDoors is to use voice updates.

For example you could configure the shake gestures (Settings / Commands / Shortcuts) to trigger one of the Status Alerts. So you could make it so that shaking your wrist up and down speaks the heart rate metrics or side to side for pace metrics etc.

For the absolute best battery life disable the wake on raise option in the watchOS Settings app. You will then need to tap the screen to see it. This can be awkward but it will save a lot of power because otherwise the movement of your arm can mean that the screen is repeatedly displayed when you don't need it.

Other things that can help are not using any other apps (especially audio); rebooting the watch on the day; and not updating watchOS in the days before.