Battery drain - what is causing it?

[Dschubba]

Correction vin was 21170 approx with an R for 2024

 

[onuraiu]

Update to my "case", today is 25th of July and dealer measured (my Victron totally disconnected):

So 5 days ago those numbers were:
main: 12.5V
aux: 12.84V

Now those are:
main: 12.8V
aux: 12.39V

meaning, main battery went low and was charged from aux.
main: 12.5V +0.3V -> 12.8V
aux: 12.84V -0.45V -> 12.39V

To sum up, according to dealer that is all OK and nothing is wrong.

 

[onuraiu]

So after I got my car back, I planned to do a longer idle test at home, but unfortunately my neighbour got stuck in forrest with his range rover and needed help from my Track-Thor .
Anyway 29th of July at 8.40am I had disconnected my victron and aux battery (took off the cables from battery) - so there wasn't any my own things connected to the car and also charging from aux battery was disabled, as aux battery was not connected anymore.. Although I didn't know how to disable c.tech device..
I measured voltages:
main battery 12,68V
aux battery 12,94V
I locked the car from remote.

On the 1st of August at 3.45pm (3 days 7h 5min later), I opened the car from remote and measured voltages again:
main battery 12,27V (0.41V drop)
aux battery 12,85 (0.09V drop)

So during that 3d and 7h, main battery lost 0.41V... my calculation tell me that, if I go to airport and leave my car there approx 3 weeks and return, then most probably I won't be driving home without help from booster...

Next I'll swap batteries when longer idle period comes again.

 

[Dschubba]

So after I got my car back, I planned to do a longer idle test at home, but unfortunately my neighbour got stuck in forrest with his range rover and needed help from my Track-Thor .
Anyway 29th of July at 8.40am I had disconnected my victron and aux battery (took off the cables from battery) - so there wasn't any my own things connected to the car and also charging from aux battery was disabled, as aux battery was not connected anymore.. Although I didn't know how to disable c.tech device..
I measured voltages:
main battery 12,68V
aux battery 12,94V
I locked the car from remote.

On the 1st of August at 3.45pm (3 days 7h 5min later), I opened the car from remote and measured voltages again:
main battery 12,27V (0.41V drop)
aux battery 12,85 (0.09V drop)

So during that 3d and 7h, main battery lost 0.41V... my calculation tell me that, if I go to airport and leave my car there approx 3 weeks and return, then most probably I won't be driving home without help from booster...

Next I'll swap batteries when longer idle period comes again.

The aux battery does a good job of starting the car if the main one goes flat

 

[onuraiu]

The aux battery does a good job of starting the car if the main one goes flat

Yes, it does. And it also charges main battery when it's voltages go low, meaning after a while they both might be empty if there is a problem...

 

[Logsplitter]

Yes, it does. And it also charges main battery when it's voltages go low, meaning after a while they both might be empty if there is a problem...

No I do t think that’s quite correct. I’m sure the smartpass works by stopping the pulse charging of the main battery from the second battery at a certain percentage level so there is always enough to start the vehicle. Thats as long as you haven't added any additional loads to the second battery and drained that to. I’m I guessing it cuts off at around 50%. Check the smart pass manual and I’m sure it will be in there.

 

[Lollo050968]

No I do t think that’s quite correct. I’m sure the smartpass works by stopping the pulse charging of the main battery from the second battery at a certain percentage level so there is always enough to start the vehicle. Thats as long as you haven't added any additional loads to the second battery and drained that to. I’m I guessing it cuts off at around 50%. Check the smart pass manual and I’m sure it will be in there.

Smartpass cut less than 50%, lowest SOC what I have seen, was 0% on main battery and 7% on auxiliary battery. And the Grenny started normal.

 

[Airleader]

My experience and the dealer’s statement (unbelievable):

Email history explains everything (Translater, and to read from the end):

Hello x,

I'm pretty thick-skinned when it comes to the - let's say peculiarities (AC, DAB, ...) - of the Grenadier, but here I can't accept it!

My BMW GS with TFT and all accessory packages is not exactly outdated either. It also stands in the carport all winter without trickle charging and starts perfectly after 6 months.

I once asked someone who works at Mercedes in Sindelfingen in the ZNA (Zentrale Nacharbeit = central follow-up) for his opinion:

Quote:
> Hi (me),
> I don't know that either.
> If the vehicle is ready for series production, no error message should appear to the driver even after the battery has been disconnected.
> However, it is normal and inevitable that errors occur in the control units due to undervoltage, but as I said, it is not obvious to the user.
> The quiescent current is also not normal and, in my eyes, not a reasonable condition because, as your service advisor already said, you would have to install a trickle charger.
> Not everyone has permanent access to a shore power supply with their car....
> I guess there is simply a lack of maturity on the software side and there was savings in development, or your workshop is not the most competent or is hiding something from you (ECU hardware outdated, would have to be replaced) or or...

I wouldn't want to formulate this so drastically, but I would like to have a different solution than a trickle charger (airport parking space?) for about 3 weeks of driving break?)

LG, (me)

PS: eCall error deleted itself after 1 day although capacity was below 50% and "battery level low" message... I don't understand, it wasn't like that in Morocco.

Greetings from the Black Forest


On 15.07.25 at 16:37 X wrote:
> Hello (me) ;
> every modern vehicle has a quiescent current
> after about 3 weeks is an undervoltage
> that's normal
> ECall cannot be deleted without a tester
> there is no other option
> do not install switches
> Do not disconnect the battery
> else the same and other errors come
> the only thing is to install or connect a trickle charger for a longer period of time
> then it works

> best regards
> X
> Service Advisor

> Hi X,
> I was on vacation with the motorcycle for three and a half weeks and then wanted to start the Grenadier afterwards, what just barely worked. However, battery capacity 0% after that and again eCall error...
> It doesn't go away on its own. And coming by every time is also annoying. Is there no other method, for example disconnecting the battery overnight or something?
> Also, why is the battery dead after three weeks? What can be done about it? Install a switch that disconnects the battery?