I'm making a wild guess here, but do you run the battery down to 30% or less? (Using the phone from waking up to "end of the night" is usually longer than most batteries can comfortably run the phone they're in - unless you don't use the phone much. But if you're using it normally, you might even be draining it down close to zero, and that can cook a battery in a month - and that sounds like the state of your battery. (Lithium batteries aren't used because they're deep-discharge batteries, they're used because they're light [the only lighter metal is solidified hydrogen] and they can be made thin. If you want to keep the battery running more than a couple of months, charge it when it gets down to 40%
and stop charging it when it gets to 80% [charging it to 100% isn't great for lifespan either].
GSam Battery Monitor makes it easier - you can set alarms at 39% and 81%. And, if you want it even easier, install
Magisk and the Magisk Charging Switch and set it to 80 40. Then you can leave the phone plugged in all day at the office and it won't charge beyond 80%. Or if you want a full charge to go home on, plug it in an hour or two before you leave and it won't start charging until it drops to 40%.)
