High discharge

When cold weather comes, countless BMW forums are full of messages regarding problems with electricity supply.

In this entry – about two messages in CCC/CIC:


Increased battery discharge while stationary

High rate of battery discharge


Despite to apparent similarity, each of error messages is significantly different. Both cause and solutions of them are fundamentally different. So – read this entry, to know, what to do and how to waste money and other resources.

These error messages can appear simultaneously (both together), so it’s very important to understand – does one problem (which) should be solved, or both of them needs attention.

Attention: if message Increased battery discharge while stationary appear after short off state (less than 15 .. 30 minutes), please refer to recommendations relating to High rate of battery discharge first.


Let’s start with:

Increased battery discharge while stationary

Every time, when the car is locked, during 15 .. 40 minutes (depending on model and equipment of the car) gradually all electronic modules are turned off – they “fall asleep”. Accordingly – the current (energy), consumed by car, is reduced. This reduction is from several tens of A to around 10 .. 30 mA, it means, around for thousand times. If some of the modules don’t go to “sleep” in time, CAS (Car Access System) module gives the command to all modules to “wake up” and “go to sleep” repeatedly. CAS wakes up everybody – “patients” and also healthy “customers”, to give a sleep medicine to everyone – sound’s quite funny, but exactly that is the procedure. If several such tries still don’t succeed, CAS disconnects complete groups of modules (using MPM – Micro Power Module, if such exists, or directly and using JB – if the car doesn’t has MPM). In this case in CAS memory the corresponding error messages will be recorded, which will inform – putting to sleep has not succeeded.

Notification Increased battery discharge while stationary means: due to some reason the car (one or several its modules) has not to succeed to “fall asleep”. Causes of this problem can be very different: starting with not completely closed doors, unclosed glove compartment, continuing with technical problems of some module (for example, a phone module, SOS system etc.), and finally – CAN (data exchange) interface problems etc. To find the cause of no-sleeping car, at first check, if all doors, luggage compartment etc. are closed. If simple solutions don’t give a result, get in touch with an experienced electrician.

Note: sleeping problems of the car can be caused also by defects of IBS system. So, if there are error messages regarding IBS sensor (also – alternator; BSD data interface), the battery is not registered – this problem should be solved immediately!


Second notification

High rate of battery discharge

means: SOC (State Of Charge) has reached low (below 40 %) range. This problem can have several causes:

  • unregistered battery. If the battery is not registered after installation, this notification can appear (and very often – also appears) even then, if the battery actually is in excellent technical condition;
  • bad technical condition of the battery – low capacity. Situation: if the battery has been registered after replacement, but is already worn;
  • increased current consumption of the car at sleep condition. This problem is described at the beginning of this entry. If CCC/CIC displays also notification regarding increased battery discharge while stationary, the problem of not-sleeping car has to be solved at first hand. If the car doesn’t fall asleep, low SOC is a logical consequences-even best battery will get discharged;
  • driving profile. In cold time, when driving short distances or spending a lot of time in traffic jams, the battery is not charged, but slowly discharged. About this problem, I will tell in details in continuation of this entry.


To understand, where the problem hides, very shortly I will tell about the alternator.

Alternators, which are used in modern cars, are AC (alternating current) 3-phase generator. It’s clear, that – if the root of the generator don’t turn, it doesn’t produces electricity. But, if the rotor of the alternator turns slowly, it’s power is reduced. Max (indicated on the body) current is reached only by higher RPM. The significant parameter, which describes an alternator: maximum current vs RPM.

Here, as a sample:

This graphic describes a typical situation. As we see, max current of generator reduces below 3000 .. 4000 RPM. Of course, this problem is known for car manufacturers, so the supply of generator is made in a way, that it’s RPM would be higher than engines RPM. But, even if the ratio of 1:2 is chosen (it means, the alternator turns 2 times faster than the engine), in idle the alternator will rotate with around 1200 RPM.

When alternator turns with 1200 RPM, it’s (typically) is able to produce max 20 .. 30 A high current. In turn, the car can consume much more current! In winter time, the situation is made worse by:

  • heating of seats and steering wheel;
  • heating of mirrors;
  • heating of windows;
  • additional saloon heaters (for cars, which are equipped with diesel engines) etc.

Together with these consumers, the total required amount of a current can reach even 50 .. 70 A. Wher to get the missing amount?

Missing amount is taken from the battery! So, for example, if the car consumes 50 A, but the alternator is able to produce only 30 A, missing 20 A will be taken from the battery. So – in idle the battery is not charged (as we can expect that), but – discharged! In this example – during half an hour, the battery will be discharged for 10 Ah, which will reduce it’s SOC for 10 .. 20 %. Of course, as soon as you will start the movement and RPM will increase, IBS system will try to charge the battery, but – if the traffic jams will dominate, the battery will be gradually discharged!

At the moment, when SOC will drops close to 40 %, IBS system will start to limit usage of the energy. For the turned on car – the heating of windows and mirrors will be reduced (or even turned off), electrical heating of saloon also can be reduced or turned off, as other similar “not important” consumers. Switching off the engine, the multimedia system will be turned off immeadiately, also other units.

Unfortunately, E6X/9X and cars of the following series are richly equipped with electronic systems, which are consuming more energy, than alternator is able to produce in idle. So, it’s very important to take into account several things:

  • to keep the SOC of car’s battery in the correct range (at least 60 %), regularly perform longer drives (at least one or two hours);
  • if such drives are not possible, regularly (especially during winter), charge the battery with a charger;
  • the battery has to be registered, and IBS system – in working order.


In forums, I noticed quite a popular activity in case of appearing these notifications – disconnecting the IBS sensor. After this operation typically two messages appear:

  • “everything is perfect, for a day or two – no notifications in CCC monitor”, and after some day
  • “who can help to start the car?”

Disconnecting the IBS sensor, the car stops to monitor the condition of the battery, accordingly – its SOC is not known, and logically – no notification will appear in CCC! But – they don’t disappear because the problem has disappeared! Logically, when the problem will become more pronounced, after several days the battery is discharged completely – and then you will have to look for help.

Disconnecting the IBS sensor – most stupid action you can take! Don’t do that!

Additionally, with disconnected IBS sensor, the alternator will work in emergency mode with a voltage around 14.3 V, which is too low, to efficiently charge the battery in winter time!


Graph: charging voltage vs temperature, IBS system: enabled


Some more suggestions, if in winter High rate of battery discharge notifications start to appear:

  • by possibility, limit the heating of steering wheel, seats;
  • purchase modern (automatical) battery charging equipment, for example, Ctek, and charge the battery on a regular basis.


Note: don’t disconnect the battery from the car, perform the charging at the terminals, which are located in the engine room. In such way, the IBS system will be aware regarding SOC of battery and will perform correctly.


At the end: example of correctly working IBS system. As you see, requested (and delivered) voltage in idle: 14.8 V!