Firmware 20.16 : battery drain keep being an issue. When will Garmin finally fix that ?

The fact that you battery dies after hitting 90% sounds a bit like a hardware issue to me. This is how my devices with a Li-ion battery usually die. I think it is time for you to contact Garmin support, they will most likely ask you to send the watch in and if you are lucky (and out of warranty) will offer you a refurbished watch for a discount. If the watch is still under warranty you'll get it replaced of course.

Well, it's appalling if it comes to this. Luckily I still have my old Fenix 5 to do the job if I have to send the watch back.

Mine should still be warrantied, 5 months... Though, I don't get how a watch can be that unstable after 2 years of production. Totally blowing my mind.

i told the garmin support that my 7pro SS (from december 2023) had always showed 18 days when charging at 100%. Right after updating to 20.16 (from 19.44) it now shows 16 days. I tried factory resetting it, doesn't change a thing. The watch still won't go further than 16 days when topped at 100% while the day before updating (and without changing any settings) it showed 18 days. They are "investigating" it

That does sound like some sort of "fault". My Fenix 7S Pro Solar is of a similar age and the battery lasts MUCH longer. I'd try the warranty route.

Chaos_White_Rabbit said:

Quite a shame for a watch that is the brand flagship and is quite pricey

yah I’m a grumpy old man who shouts at clouds but this statement (in these circumstances) is irritating.  Obviously you should be getting better battery life (assuming you don’t have some weird setup that might cause this - and it shouldn’t happen anyway). I understand your frustration at the watch and certainly Support should have got back to you but how about you contact them over and over again until you get action.  Submitting logs and then waiting months to hear back without pushing for action then posting on a user forum seems silly.  Pay $40k for a new car and find it runs only 20 miles before it shows empty and I bet you would not wait months to hear back from the dealer. 
You would clearly seem to have a hardware issue - it happens.  Support should definitely have got back to you. It happens (maybe too many times). Keep calling and emailing (calling has always worked best in my experience) until you get resolution. 
sorry for the rant. 

Well, let's see what Garmin can do for you. They are buying these (tiny) batteries from third party suppliers and given the complex chemistry eventually some will fail super / too early. Even if it is just 0.1% it'll bite people so Garmin's support response is what I would judge them against.

This is very different from all the software screw-ups which are really inexcusable. Granted, we are not talking about flight computers but constantly using their customers as beta testers is really showing either a complete loss of understanding for their code basis or a f&%!/ you attitude. 

In addition to my battery draining faster after the 20.16 update, my GPS is also way, way off. For example, today my wife and I went for a walk. Her GPS showed 3.26 miles while my GPS showed 3.02 miles. That's nearly a quarter mile or a full lap of a traditional track. Anyone else having this issue with the 20.16 update?

My watch has the 20.16 update, and I have two issues. One is the battery draining too fast. But my GPS is also substantially decreased. My wife and I went on a walk tonight. Her GPS showed 3.26 miles (Fenix 5S for her) while my watch showed 3.02 miles. Her watch is 2 1/2 years older than mine. We walked side by side, and I know her GPS is more accurate based on landmarks along our walk.

My Fenix 7 Pro gets about 13 days of battery life with about an hour a day of activities. I have the backlight set to max brightness, lots of data on the watchface, and I get a lot of notifications throughout the day. I also have a Fenix 5 as a backup so the battery is much less of an issue as I just wear the old watch when the new one is charging.

13 days is about what I would have expected tbh. Now, I resetted to factory seeting today and restored my last back up. I'll see if it changes something. Then I'll have tried everything and I'll have to send the watch back to warranty. I'm lucky to still have the 5 to do the job if I have to send the watch back, but for people who have no solution, it's a misery.