Garmin Watches Durability

  I have had a replacement under warranty 5x plus, Should be a minimum cost to replace your watch, with a refurbished one from Garmin, I think they said £180 to me, but could be wrong, yes it's expensive, they should repair it for free, keep at them say how disappointed you are, raise it with a manager, get a discount, if you don't complain and make a stand they like all companies will take your money, Make a stand. 

My watch had many issues but there is a standard fee for replacement out of warranty in the UK, even if you bought a second hand watch and it went wrong you could pay a certain fee and receive a refurbished one, to get a watch repaired out of warranty , doubt it would be worth it.

Interesting! What is the rate to replace this watch with a refurbished one in the UK?
I have repaired some garmin watches of friends / relatives, spending from 10 to 50 euros (out of warranty)

As to durability, generally excellent. I have several old Fenix-es aged between 7 and 11 years and they are still working perfectly. In some I replaced the battery, that's all. The cost of out-of-warranty repair or replacement I find quite reasonable. Heaps cheaper than a new model, and often even cheaper than buying a used one, plus you get warranty on it (how long depends on where you are). Call Garmin and ask them. In my experience they are very helpful.

Very good feedback from everyone here, I appreciate that.

I actually followed Niccolo B. advice (Data also mentionned it), 25¥ battery on taobao (Aliexpress equivalent here), watched a youtube video on the operation and successfully replaced the battery.

Operation realized yesterday and this looks like a successful repair. I can record activities again and everything seems to be working like they should be.

So it seems to me that Garmin repair shop (at least here in China) does not consider changing battery for Fenix 5X plus model
This operation requires that you peel the glued battery off from the mother board, a bit finicky and risky but nothing very doable.
Garmin repair shop seems to simply go for a motherboard replacement, charging almost 100 times the cost of the single battery (2,440¥ vs 25¥)
This policy is probably more motivated by ease of replacement rather than profits

Lesson learned here, if you get a +200$ quote from Garmin repair shop wanting to change your watch motherboard, you can first try to swap in a new battery by yourself with the help of some YouTube video and if you are comfortable with your skills.

Looking back at it, aside from accidents and just like smartphones, it's only normal that the battery is the first component that need replacement after 4 years

Now I'm happy with the forum feedback and the result out of it but still unhappy with the Garmin repair support.

very well! I'm glad to know that you solved the problem

I bought my garmin on Sep 2019 and, after replacing the battery, I'm still having problems with it. It was commented here: 
Fenix 5S Plus sudden increase in battery drain - fēnix 5 Plus series - Wearables - Garmin Forums

Any ideas? 2 days of use, without any workout.

Yes! Try changing the USB cable.

I had this problem and I noticed that the pins of the cable were burned if I zoomed them to 20x

it was not visible without magnification [look at pic right]