No noticeable impact on battery life.
as a normo you would think it does. But apple have done some great work so it only actually updates the complication when you need it to. Even without the complication it’s constantly reading the elevation and doing it’s math so power is used. Complication or not.
top tip to those looking to squeeze ever second of battery out of their watches....STOP! Stop turning your amazing watch into a 1980’s Casio. The battery will easily last a day and then some (40hrs on my AW6 with everything on and using Siri and more).
don’t use a battery complication. The drain is near linear and won’t suddenly die on you. /EndRant