I got a Fitbit as a gift, it lasted 18 months, Fitbit replaced it under warranty, that lasted 18 months.
Before the first one died I bought one for my girlfriend and that lasted 12 months. A friend of mine had their slightly more advanced watch with the colour LCD and the battery lasted just over 2 years, now it will run the watch for about 10 minutes before dying.
Will never touch the things. Utter crap build quality, and the software is rubbish.