611? Have never heard about this before. Is it calling the mobile provider or the vendor of the device?
Mobile provider. Make sure you do it with the "bad" sim In the U.S. It is 611, might be different elsewhere.
Folks! That was it! Really! I've for this testing both SIMs enabled since I posted the above, and in that timespan of 9 hours it ate only about 7% of the battery! Meaning, now it could be that the battery will last even longer than the said 4 days! When using the following formula then it says that the battery should last 9 / 7 * 100 / 24 = 5.35 days. Btw, as said it's a cheap smartphone, model is "XGODY Note 10", unlocked (ie. not bound to any mobile provider), upto 4G (LTE), with dual SIM, old model of 2020 or even 2019 as I recently saw that they ship it now with more memory (both RAM as well flash). It has a big display of 7.2", but the cameras are not that good as my ancient Samsung S3 had better photo quality than this one :-( There are nowadays also other such similar cheap 4G products below $100 (on eBay I had paid for mine even only about €75 or so IIRC, it's of course a new product, not a used one), and I just saw a similar cheap one with even 5G for under $130 (or was it €130 ?), will need to research it... Of course these are the cheapest China smartphones, but that fact doesn't matter for me as I don't discriminate anybody, and it's also good for my limited budget...
Those charge indicators are usually not really accurate. It is best if you continue the test until the battery is empty and the phone shuts down. Having said that, it does look like that you found the source which caused the battery drain.
There are location based apps that let you script things. You dont even have to go airplane, turning off data will save a lot of power. I wonder if anyone ever said "Wife went full airplane on me for buying a new rifle"
The test now runs for 16.783 hours. In that time the battery went from 75% to 61% : Code: hrs = (19 + 20/60) - (2 + 33/60) = 16.783 # using CET times batt = 75 - 61 = 14 hrs / batt * 100 / 24 = 4.995 days Ie. it stabilizes at almost 5 days. I would say we now can safely close this case. Thanks to everybody for the help and suggestions.
How to Turn Your Old Smartphone Into a Portable Media Player https://www.lifewire.com/turn-smartphone-into-portable-media-player-4125165