After couple of weeks wearing the watch I've noticed that CR2450 doesn't really fit the device - it's nominal voltage (3 V) is really just above a threshold when the watch stops working. I've checked and found out that it turns off when voltage drops below 2,9 V and it's quiet an issue, because CR2450 nominal capacity is calculated from 3,0 V to 2,3 V. Sometimes you can even buy this type of battery from the store when it has less than 3 V left. 

So I decided to change CR2450 to rechargeable LiPO battery with 300 mAh capacity. Besides ability to recharge it, it has a short circuit protection built-in and protection from overdischarging - it cuts output when voltage drops below 3 V. And it works very well! I have short circuited my watch few times accidently when washing my hands or in the rain and protection worked. 

P.S. it feels better for my whrist to wear the watch with a new battery :)