It is a bit puzzling that you could see the 4G indicator but no LTE, both your OnePlus 5T and CSL support LTE and VoLTE:
Hardware stats for your 5T (click on
Expand in the
Network section to see the complete listing)
https://www.gsmarena.com/oneplus_5t-8912.php
Band/frequency support with HCL (in
Network section)
https://en.wikipedia.org/wiki/CSL_Mobile
There's limited 4G compatibility between the two, but at least there's that:
https://www.kimovil.com/en/frequency-checker/HK/oneplus-5t
There is a chance that aspect is part of the increased battery drainage, just two bands. causing your phone to be working harder in the background as its cellular radio chip to find better connectivity. But that's just supposition. The next time you return Hong Kong, check the APN settings in your 5T. It should match up with HCL's recommended APN:
https://www.hkcsl.com/en/mobile-data-setup-guide/
Typically the APN gets automatically configured in the background when you add a new SIM card but every so often the process fails from some glitch or whatever. In that case it's just matter of manually creating a new APN entry yourself, using those exact, recommended settings.
Jumping over to the other thing you mentioned, the Google Play app using 7%. On your phone, is that consistently and significantly higher when your back in the U.S.? That does seem a bit much but given how much system resources Google's stable of bloatware require that may or may not be the actual source of that battery drainage. But if it is significantly higher only when in Hong Kong, try going into your Settings >> Apps menu, find and open the Google Play Services and Google Play Store apps entries, and use
Clear data. Using
Clear data will wipe the app's settings and config data and its cache. in these two particular instances, it won't affect your Google account data, that's always retained and maintained in your online Google account, but it does pertain to the personal data-mining data Google collects on your phone.
That is something of a long-shot though. Keep in mind the Battery option in your Settings menu is only going to display the typical installed apps and only some system-related services. That's perfectly adequate for most of us. But there's always a lot more processes and services actually running in the background all the time. So Google Play Store app might not be the actual issue when you're in Hong Kong, a more revealing option is to check
Running services. It's in your Settings menu but not showing by default. You need to enable Developer options first to access
Running services:
https://www.howto-connect.com/how-to-view-and-control-running-services-on-android/
This might reveal more to help you determine what is or isn't causing that battery drainage. The
Running services option also has a
Cached services menu so look at that too. (..... don't get too over-zealous force stopping apps and services with
Running services as some of them are a necessary part of Android's basic functionality. Use it as reference and not so much an app manager.)
