Nexus 5X battery drain (even after battery replacement)

Hi all,

I know there is already a ton of questions about battery drain on a smartphone, but I couldn't find one that matched my experience. This is particular hard to get rid of.

I have a Nexus 5X which after a couple of years started to drain the battery faster and faster. So I started to do some looking around and some troubleshooting.

• First I started to keep an eye on Android's battery stats to see if any weird app popped up, using a lot of power. Nothing out of the ordinary. Most used apps used most power, but not exceptionally much.
• Started to be more conscious about device usage. Switch wifi, bluetooth, location off when not in use. Going through individual app-settings to make sure they weren't trying to get a gps fix in the background or something.
• Since the device was a couple of years old and heavily used, I figured it might be time for a new battery. Ordered one, replaced it (yay for ifixit guides). Same story.
• Reset the device to factory settings and got rid of most apps (kept the ones I used daily because, you know, I use them daily). With fresh software and a new battery surely, things would look up? Nope.
• Hmm... Installed an app to closely monitor the battery (Accubattery). Again, no apps that stood out as exceptionally batteryhungry. After a couple of weeks of use, it did show the max capacity of the new battery was only at 75%.
• Contacted the shop I bought the battery at. They were cool, sent fresh one so I replaced the battery again. Reset to factory settings just to make sure.

That's where I'm at now. Overnight, with zero screentime, the battery dropped about 40%. I get about half a days' use out of it before it is completely dead.

Are there any other things I could be looking at? Any tips, hints? Any advice is welcome.

Thanks in advance!