The new Companion app seems to use a LOT of battery on iOS. I did a 40 minute workout yesterday and it used over 70% of the battery on a 3-month old iPhone 8!
In previous releases I’ve used the ZML app for much longer, and only seen a few % battery usage - for example I’d happily have the app running, screen on, riding for a couple of hours, and not really think anything of the battery usage afterwards.
Today I did a social ride of about an hour and saw about 20% battery drop, although more than half the time the Zwift companion app was backgrounded as I was also using Discord. On these two pieces of very circumstantial evidence my guess is that there’s something about being in the new workout screen that uses a lot of power?