Impact of WiFi on battery life?

I think wifi activates only when BT is not connected and there is something to upload or you make it to sync with wifi.

So in most cases, I don't see it using much extra.

Which is kind of annoying as the BT is slow, it would be much nicer to sync with wifi when I'm back home, not with slow BT... and then you make it to sync with wifi and it says syncing is already in progress but it's just slow :D 

Hmm, at least in previous watches I’m pretty sure WiFi sync occurred even when I had BT on (I never turn BT off and I could tell the difference in sync speed when at home in WiFi vs when out and about using BT).

In fact, if anything I would guess that it’s the opposite, that it falls back to BT sync when the configured WiFi network isn’t available (in which case the WiFi radio would need to stay on even when not in use in order to detect the configured network)

It's trivial by design, as Garmin likes to preserve the battery.  The hardest hit will be when you sync music from something like Spotify.  When you sync activities, it's only connected for a short time (much faster that BT sync). Same when you update things like FW over wifi.

Wifi isn't doing anything unless you do a manual connect or there's an activity to Sync, and when done, it turns off.

If WiFi is configured, it will only be used in one of the following reasons, otherwise the WiFi is off and not used.

1. Manually initiated a WiFi sync from the settings or control menu.
2. After activity is saved, auto sync is enabled ,and BT is not available.
3. Syncing Music from a third party music app, such as Spotify.

In either of these 3 cases, the WiFi radio will get turned on.  If a configured network is found within ~30 seconds, the transfer will start, otherwise the "no network found" message is displayed.  The radio will be turned back off once the sync is complete or no network is found until one of those 3 cases is again met.  So configuring WiFi almost no impact on battery life especially if you always have a BT connection.

My experience with 935 was that no. If bt was available no wifi sync, just slow bt sync.

And same seems to be the case with 945.

sabeard seems to have same cases when wifi is used, plus the music part that I've not using :) 

On other devices, even when BT is connected, I'll manually start wifi to get a FW update if I know there is one available. (it's much faster that BT)  For activities, it will use BT if available and won't even check for available wifi networks.

How do you manually force a WiFi Sync?

If you added wifi to your widgets carousel, simple select it and the sync will start.

I have configured hotkey for it, long press START to Wifi sync.