Charge loss while parked
Super Member
Joined: Dec 2022
Posts: 744
Likes: 224
From: Sweden
2023 EQE SUV 500 4Matic
As I mentioned long ago in this thread, I will be storing my car long-term for about 5 months in Greece during the summer/fall of this year. From reading on this thread and elsewhere, I have concluded:
1) I should leave the car with the High Voltage battery charged to 50%
2) The 12v battery is critical to many systems while the car is off/at rest, including remote monitoring
3) Some have experienced conclusively that the 12v battery is occasionally and automatically charged by the High Voltage battery.
4) Others have experienced that their 12v battery was NOT charged occasionally and automatically by the High Voltage battery.
5) I want to be 100% certain I don't have a surprise waiting for me when I retrieve my car at the end of the storage period.
6) To avoid the aforementioned surprise, I would be wise to deploy a 12v trickle charger.
7) To connect the aforementioned trickle charger, I need to open the hood (customer-forbidden area).
1) I should leave the car with the High Voltage battery charged to 50%
2) The 12v battery is critical to many systems while the car is off/at rest, including remote monitoring
3) Some have experienced conclusively that the 12v battery is occasionally and automatically charged by the High Voltage battery.
4) Others have experienced that their 12v battery was NOT charged occasionally and automatically by the High Voltage battery.
5) I want to be 100% certain I don't have a surprise waiting for me when I retrieve my car at the end of the storage period.
6) To avoid the aforementioned surprise, I would be wise to deploy a 12v trickle charger.
7) To connect the aforementioned trickle charger, I need to open the hood (customer-forbidden area).
I performed a small experiment:
- Turned on the parking lights, locked the car an left, noting in MMe that the 12v battery status was "charged".
- Checking MMe frequently, I noticed that after about an hour, the 12v battery status became "partially charged".
- I went to the car, turned off the parking lights, locked it again and left.
- Checking MMe frequently, I noticed that after about an hour, the 12v battery status was once again "charged" and my HV battery status had gone from 45% to 44%.
Bliss...
Super Member
Joined: Dec 2014
Posts: 819
Likes: 184
From: New England/Florida
2005 SL 500. 2015 S550. 2016 GLE400 2018 S560
Today, I think I answered my own question regarding points 3&4 above.
I performed a small experiment:
- Turned on the parking lights, locked the car an left, noting in MMe that the 12v battery status was "charged".
- Checking MMe frequently, I noticed that after about an hour, the 12v battery status became "partially charged".
- I went to the car, turned off the parking lights, locked it again and left.
- Checking MMe frequently, I noticed that after about an hour, the 12v battery status was once again "charged" and my HV battery status had gone from 45% to 44%.
Bliss...
I performed a small experiment:
- Turned on the parking lights, locked the car an left, noting in MMe that the 12v battery status was "charged".
- Checking MMe frequently, I noticed that after about an hour, the 12v battery status became "partially charged".
- I went to the car, turned off the parking lights, locked it again and left.
- Checking MMe frequently, I noticed that after about an hour, the 12v battery status was once again "charged" and my HV battery status had gone from 45% to 44%.
Bliss...
Super Member
Joined: Jan 2022
Posts: 981
Likes: 555
Interestingly, I was out of town for the last week. My car was charged to 37% when I left it in the garage. The temps were in the teens for three of the days I was gone, although my garage is usually much warmer than that (although not heated, it is insulated). I did experience a 1% drop in charge level on the high voltage battery during the week I was gone. Usually it maintains the current charge completely when I have the one week absences, so this was unusual.....but it was very cold last week.
Super Member
Joined: Dec 2014
Posts: 819
Likes: 184
From: New England/Florida
2005 SL 500. 2015 S550. 2016 GLE400 2018 S560
You are correct. Took vehicle in and was told 12 v battery has failed and replaced it with a new one. Going to pick up car tomorrow morning. I see the dealer just connected car to a charger putting out 3.2kW. Says will be charged to 90% by 9 o’clock tomorrow (26 hours).
Senior Member
Joined: Mar 2023
Posts: 368
Likes: 136
EQE350 SUV 4MATIC
Been away for just over two weeks. The car is in underground parking about 5-10C, and not plugged in. When I left the SOC was 45% and range was 160km. The reading was the same after a week. At the 2 week mark it was up to 47% and range of 178km.. Go figure.
MBWorld Fanatic!
Joined: Feb 2014
Posts: 1,938
Likes: 396
From: Iowa
2025 EQS580
I bet it’s temperature related. 10 degrees C is a lot warmer than 5 degrees C. At the end of two weeks the temperature was probably closer to 10 degrees C and that’s why the range increased.
Super Member
Joined: Dec 2022
Posts: 744
Likes: 224
From: Sweden
2023 EQE SUV 500 4Matic
A follow up post on my experience, in case this could be of use to anyone else.
I parked my car in storage in Athens for 3 1/2 months with a trickle charger on the 12v battery.
The main battery level was 49% when I left it. It was 48% when I picked it up. I was impressed, to say the least.
I'm sure it would have dropped more had I not used a trickle charger on the 12v battery and let the main battery occasionally re-charge the 12v battery, as it's supposed to do. How much more, I do not know.
I parked my car in storage in Athens for 3 1/2 months with a trickle charger on the 12v battery.
The main battery level was 49% when I left it. It was 48% when I picked it up. I was impressed, to say the least.
I'm sure it would have dropped more had I not used a trickle charger on the 12v battery and let the main battery occasionally re-charge the 12v battery, as it's supposed to do. How much more, I do not know.
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