my brand new Nokia 1 Dual Sim, after a full recharge, gets fully discharged in 15 hours just by staying in stand-by (phone is not used, just left it on a shelf). The phone was hard reset fo factory defaults, has no additional app installed except those pre-installed, GPS is disabled, Wi-Fi is enabled and configured, 4G data is enabled, Google account is configured. Installing the 06-2018 Android security patch does not solve.
But just 15 hours in stand-by compared to the 15 days declared on the Nokia website make the telephone not usable even for a single-day usage.
I think the stand-by battery life should be much higher than this!
Do you think there is some hardware problem?
Sometimes a new phone might need a couple of charges before it stabilizes. After a phone reset all the installed applications are compiled in the background which too draws up power. If the signal on the SIM is weak that too contributes to faster power drain as the phone is trying to connect to the tower trying to get better signal. I too face this issue. If I am in a place where the phone signal is weak then the battery discharges more rapidly. The 15 days figure is unrealistic. If you keep the phone in flight mode then it will last longer, but what is the use if you cannot make and receive calls. Check how the battery charge-discharge is doing after about using it for a week.