Garmin Fenix 3 bought in late 2015 - still going strong.

Used daily (not while sleeping) and aside from weekly running, it has seen plenty of seawater swimming, lake dips, kayaking action, plus daily showering, etc. over the years. No major issues, but the original charger (wall electric socket plug thingy) stopped working 3 years ago, and now i charge it from my Mac via a, new, charging cradle and cable.

The battery is still satisfactory and needs charging every 2 to 3 days. The only issue I have to keep an eye on is that when it is disconnected from the Mac it sometimes freezes and needs to be switched off and on again (seems to be a cure for so much in life!).

Also, despite there being an indoor rowing widget, it really doesn't work well at all for this activity.

Useful tip for some OCD fit-biters - wearing it while horse riding quadruples your steps count