FR645 or FR935

I could've sworn that I read that optical HR equipped watches that can charge during activity turned off the sensor while connected to power. I know that in standby/watch mode the sensor turns off when charging so maybe I just implied, to myself, that this was the case during an activity.

The optical heart rate sensor is shut off while charging. If wanted to charge on the go, and get heart rate, it is recommended that a Heart Rate Monitor strap be worn.

Good to know I wasn't making up/imagining things.
It hasn't been as issue for me wither way and as of now I don't have anything on my radar that would require charging on the go but it's still good to know the what and how of the devices I use and comment on.

R_Tellis. Interesting. On the 935/f5/va3 it would make sense to turn off ohr when charging, as you can't charge while it's on your arm, but I wonder about the ones where you can keep wearing it.. Maybe it varies if you have the USB mode set to Garmin

OHR lights shut off if the device is in USB or Garmin Mode. I have requested some information from the teams to get some more information about if this might be possible in the future. I'll report back when I get some more information.

We sound like we are in the same camp. I've been toying with the idea of the 935 for a while, but I find that at it's current price it is just too much watch for my needs (size and multi-sport). The VA3 is a good daily wear for an avid runner, but I due to limited battery and surface level run features, it is more of a casual enthusiast watch/smartwatch IMHO.

The 645 is basically the 935 minus the multi-sport and minus the 24hr battery wrapped in a smaller case. That makes the 645 a sweat spot win over the 935, especially for daily wear including slipping under a dress shirts.

The only potential rub I see with the new 645 is the claimed battery life. We have proof that Garmin overstates the battery life in the VA3, so I'm concerned that the 645 may perform at that same level (VA3 = ~30 GPS miles weeks). If that is the case, the 645 will basically become an overpriced VA3 with deeper running features. To that end, it may makes sense to wait for 935 prices to slip and the 935 will become the all around better buy, but not a daily wear.

In short, if the battery life of the 645 is solid, it could be the best of both worlds between daily smartwatch (VA3) & feature rich long life of 935.

The OHR sensor is disabled while charging due to the potential for inaccurate heart rate data while attached to the charging clip. The watch will be slightly lifted from the skin and increase the potential for outside light pollution.

If charging on the go it is recommended that a Heart Rate Monitor strap is used.

First of all: I didn't know, that the FR 645 has WiFi and a barometer. And neither did I know, that the screen size is the same like in the FR 935. Sorry for this. I didn't inform myself enough.

The other points:
.) I still think, the FR 935 look better. Optically it looks like the space grey Macbooks Pro (although it's plastic). I don't like the silver ring of the FR 645. Therefore I recommend the FR935. I owned the base line Fenix 5s and I didn't like the silver ring too.
.) FR645 has no touch screen: this isn't an argument for the FR 935, it's an argument against the FR 645. Why? Because the FR 630 had this feature. Since the FR735 I personally like buttons more, but there are people who hoped, that the FR 645 has again a touchscreen. So: one feature of the FR630 is gone.

In my eyes the FR645 connector isn't an advantage, because you are discussion a workaround because of the rather poor battery time (compared to the FR 935). The better solution would be a better battery time -> FR 935.

Something which would be really great is, if the 4 GB storage of the FR645 could be used for maps (like in the Fenix 5X). But at the moment it's a smaller and not so good looking version of the FR 935, which will lose it's value pretty fast.

Conclusion: keep the FR 935, it's a great watch and except for music, touchscreen (when you need it) and maps (like in the Fenix 5X) nothing is missing.

Conclusion: keep the FR 935, it's a great watch and except for music, touchscreen (when you need it) and maps (like in the Fenix 5X) nothing is missing.

Yeah i tend to agree with this, unless the smaller size and aesthetics are really important. Mostly since the OP already has a 935 (and i assume they're otherwise happy with how it works).

So my partner runs tris, I do not.. I have a 935, she has a 235. Thinking about a 645 for myself and giving her my 935; I haven't ran with music in years, so that's not a concern. Thinking I'd miss the ridiculous battery in the 935... I don't mind the size/weight of the 935 at all, and to me it's the perfect watch, though overkill for my needs (I literally only use outdoor biking, cross country skiing, yoga, and running.. no need for multisport at all). Can anyone think what else I'd give up by parting with my 935 and going with a 645 instead, besides battery life? I don't run ultras, the longest distance I run is 26.2, so I'm not worried about the battery dying mid-race. I read DC Rainmaker's preview, but can't figure out what else the 645 would be missing that I'd use.

Sounds like you would be fine with the 645 then and your partner will love you even more!