I don’t know how your car manages with a 12ah battery my motorcycle has a 14ah battery!!
My EQA has a 64ah battery and because I have a dashcam which runs when parked I fitted a battery monitor, it has shown the battery dropping to 40% or less on numerous occasion, probably because I do short journeys and I have a 22kw charge point which don’t give enough time to charge the 12volt battery. This means I have to charge the 12volt once a month or so. I have found the Mercedes me app has only once shown a warning to charge the 12volt battery and it doesn’t give any advance warning that the battery is getting low, insisting it is fully charged right until it’s less than 40%.
It def is the battery for my car as I did a no plate test. And on the same site the same battery comes up for the EQA………of course these batteries do not have to suffer the power drain of turning over an ICE engine they are only there to run items when the main lit-ion battery is not in circuit so to speak. As I understand it this battery’s job is to run things like lights and ancillaries when the high voltage battery is not connected ie when the car is not switched on to ready mode.
On one of the EQ screens you can see a breakdown of the consumption of the car between driving, heating cooling and other consumption. I assume the other is all the ancillary stuff running at the time and the recharge of the 12v battery and it can be as high as 8% but also lower. As an aside yesterday it was 20deg outside the same temp as the interior setting and the heating/cooling system was showing 0% consumption.
I take your point re the app and the level who knows what measurement they have programmed it for but it certainly is different to my e class (a 2018 e220d estate) which often showed partially charged and nagged me during our lockdowns.
On your issue of needing to charge your battery reguarly I have seen many other drivers do that in the Hyundai, Kia’s and Renault marks particuarly. Frankly I would not be a happy bunny if I had to faff around like that with what for me was a 90k car (I genuinely could buy a house for that money!).
I do use my car for lots of short journeys and it may not be used for 2 or 3 days in a row with only a 8km return trip before it stands again and so far no issues over 9mths how that progresses we shall see.
I wonder if the dashcam itself is what is draining the battery if it is running all the time one would not expect such a small item to do so but I am not an automotive electrics expert just a punter who has an enquiring mind on how these things work😉I look forward to the day when I can finally have a dashcam built into the car and the Tesla system does appeal about the only thing Tesla offer that does appeal actually😉
I too was surprised at the size of the battery but clearly Mercedes’ have a lot of experince of these deep cycle battery's used to run the ancillaries and it has to be said many were surprised there even was a 12v battery in an electric car when you have the large lith-ion one used to power it. But it does seem when these batteries start failing they do cause all sorts of difficulties and it seems to me we will have 2 main intial reactions when an electric car starts giving funny messages or will not power up, switch off and switch on again ie ctrl alt delete or replace the 12v battery the cry all so familier on many of of our other electrical consumables🤣