Short battery life

Hi,

I got a instinct Crossover Solar quite recently and I'm almost completely happy with it. 

The only issue I have, is that the watch drains the battery much faster than expected. I use it only in SmartWatch mode so officially 28 days are expected. After recharging, the watch shows even 30 remaining days but goes every day 2 days down. So after 1 day it shows 28, after 2 26 and so on...

So in the end the battery only holds for around 15 days. Does anyone else have this issue? Is maybe my battey broken? How long does your instinct crossover work before you need to recharge (if you have one)?

Thanks!