Hi bro .
I have ultra watch 
1 which i bought 1 year ago currently 400 days passed and i noticed no battery 
percentage drop i mean still its 100 
percent health … unmaiya naan nalla maintain panrena or athu nalla iruka nu therla …
3 day varuthu battery
and in upcoming months sudden reduce could happen. dont worry. it will auto adjust according to your usage.