Chosen Solution
I bought my phone in 2014 and suddenly battery drains A LOT faster than usual. But i’m not sure whether this problem is related to battery or logic board. :(
Considering your phone is nearly 3 years old, I would change the battery first. If you have a Mac, download coconutBattery to test your battery. On a PC, download 3uTools. Look at the design capacity or design maximum charge. If that number is lower than 80%, then your battery should be changed.
