I am in the same boat... I have tried running my week old J7 Prime in Safe Mode for a few hours, but the battery is not even lasting 18 hours (with minimal usage)... Running the phone in what I call "bare bones" mode is hardly how they should be run!!! My previous J7e lasted 36 hours in normal usage mode....
I don't think the 3300Mah batteries are half as godd as the previous models!
have you tried putting the device into Safe Mode? Safe Mode disables all 3rd party applications and helps us determine if the issue is caused by an app misbehaving or software. If you haven't, please follow the steps in this link to place the device in safe mode for 2-3 hours: Boot in Safe Mode and monitor the battery usage during this time frame for any changes.
I found this thread searching for why my battery started draining over night. I got an update about 3 days ago and like an above user said, after that length of time my battery drainage started. I thought the most annoying part of the update was the resetting of all my notifications and opting me in to new features. Nope, this is!
Went to bed with battery at 100, woke up it was at 64. Usually at 99/98. I have done the suggestions in this thread. Cleared caches, taken out battery, and went into safe mode for a couple hours. If I'm not connected to a charger I get rapid drainage. I checked what apps were using the battery and nothing was draining it, or using more than their normal smidgen. Even shutting them off, made no difference.
This is ridiculous. I cannot now rely on my cell's alarm to wake me up cuz the battery might die unless I have it plugged in. I can't live life tethered to a charger. What in the world did this update do to batteries??
Go to settings > apps > Google play services > storage > manage storage > CLEAR ALL DATA, restart phone and you are done everything will be normal as before, I was so frustrated of this problem a few days ago, even bought a new battery but nothing changed, called customer support and they asked me to reset my device would solve the problem but I didn't reset my device got lots of important data all I did was reset Google play services app storage everything is fine now even tested the old battery and it is working fine, just wasted my money by buying the new battery