I had a Garmin (2 I think it was) and loved that thing. It had to be opened to change the battery, but it lasted for months and was waterproof. I never took it off. My only gripe was the bands would wear out faster than the batteries, and you'd have to buy more and keep replacement bands on hand because they would just suddenly "go" one day. I lost my Garmin because one time in Hawaii, I turned my back to the ocean and it threw a 15 foot wave at me out of nowhere, which sent me flying and twisting. I am VERY lucky that I instinctively put up my hands, and bent at the elbow, because I ended up upside-down landing on my elbows in shallow water. That would have been my head if my elbows weren't there. The strap broke on that impact and the water took it.
Damn,,, that's a wild story. You should get a new Garmin watch, they are even more awesome now.
I looked for 2 or 3 years after it happened and all of the models were needing to be plugged in to charge (which I really don't want) and not waterproof. If that still the case?
You could get an Instinct Solar, put it in battery saver mode. As long as it gets 3 hours of sunlight a day it should last forever.
You'd be turning of all the smart watch features though.
Instinct Solars are the way to go if you want battery life. It's nice to be able to top up your charge just by being outside.
Mine does plug in to charge. But it is extremely water proof. It does so much stuff too. Really too much for me to list off here. You should go check out the Fenix lineup. I have the Fenix sapphire solar and I love it.