Replacing the battery

There are a lot of different opinions regarding coding and registering the change of the battery, but it’s impossible to find exact and correct information.


In this entry, I will gather information, which can not be found in BMA AG materials (links to them – at the end of this entry).


To make it easier to understand, how does the IBS and all battery management system works, I suggest to view it in the following way. Let’s suppose, that we have a small “business” – we supply water for the neighborhood. The water is accumulated in the tank. By one pipe we fill the thank, by other – when necessary, pour it out. The tank is our battery. The amount, how much we fill/pour it – we see/know (it’s measured by IBS). The tank is opaque – we don’t see the fulfillment visually (the same is with a charge level of the battery – we don’t see it directly).


But we can use several tricks, to find out, how full the tank is.

At first – we can evaluate, how strong is the jet, when we open the tap. This test would be equivalent to measuring the voltage of the battery on the clips. Unfortunately, this measurement is not exact – a significant decrease of the jet we will see only then when there will be very small amount left in the tank – the same is with battery: a significant drop of the voltage can be seen only then when the battery is already practically drained.

To increase the precision of this measurement, we can regularly drain the exact amount of water and measure it, comparing to the etalon. This is exactly the way, how the battery management system works -“takes” the exact amount of energy (Ah – amper hours) from the battery and measures voltage on the clips before and after this process.

We can “knock” by the tank – the hollow the sound, the fuller the tank. This is exactly the same way, how the battery management system “knocks” the battery – measures it’s inner resistance (chemical efficiency).

We can take into account, that the tanks clogged by time, and each draining decreases the mechanical efficiency of the tank. Exactly in the same way the battery management system takes in account aging of the battery (which is proportional to its life cycle, increases – when the temperature increases, when starting the car, etc.)

We can calculate even evaporation of the water – equivalent of self-discharge of the battery.


Why is a such complicated control system necessary? In the sample with water supply: if the tank is overfilled, the water will pour over the sides – will be lost; if the tank will be empty – our “business” will suffer. It’s similar to the battery – if we will try to “overload” it with too much energy, the excess energy will transform to the heat and will damage the battery. But if the amount of energy will be less than necessary – we will not be able to start the car.


Two basic parameters define the viability of our “business”:

a) SOC (state of charge) – parameter, which defines, how full is out tank (battery);

b) SOH (state of health) – parameter, which defines, how usable is our tank (battery).

Additionally we can measure a lot of additional parameters: flow rate of the tank while draining the tank rapidly (availability of start current); balance of the tank during every day, especially putting the accent on the moments, when at the beginning of the day there was more water (energy) as at the end of the day; register the fulfillment of the tank (SOC) at the end of each day, calculate, how much water (Ah) has flowed thru our tank.


I think the idea of, how IBS manages energy is clear, and further, I can use terms, which relate to the car industry.


Shortly about each of parameter: SOC and SOH.

SOC, 100% – fully charged battery; 0% – fully discharged battery. This parameter (as explained before) – is not “seen” directly, but is calculated, using many tricky ways. That’s why it’s very important, that all necessary parameters (current, voltage, temperature, aging parameters of the battery) are true. If even one of the parameters will be faulty, SOC data also will be faulty – trouble is guaranteed.

SOH. Idea: 100% – perfect (new, with full capacity) battery. 0% – totally wore out a battery. Unfortunately, BMW AG doesn’t give any information, which parameters are used to calculate SOH. There are many parameters available, in addition to mathematical calculations: voltage on battery clips, it’s drop; the inner resistance of the battery by low loads and in the moment of starting the car (high current). After it’s calculation, SOH decreases with fixed “speed” in proportion to it’s usage time (hours), additional wear is calculated when the car is started. The speed of aging depends on temperature when temperature increases – mathematically the battery ages quicker. In addition to the fixed speed of aging, the system can “speed” it up, if it’s real parameters (a drop of the voltage, when battery discharges, inner resistance etc) shows, that the performance of battery decreases faster as predicted.


After it’s determination, SOH can only decrease! It means – even installing a new battery, SOH will continue to drop, if the new battery will not be registered – calculation of the energy will be totally wrong!

What does SOH, for example, 50%, means? Wery simply – if the car has, for example, installed battery of 90 Ah, it’s management system will use only 50% of batteries full capacity (if SOH is decreased exactly by measuring remaining capacity) of only 45 Ah. If a new battery of 90 Ah will be installed and not registered, half of it will not be used! It means, the battery will be in the partially discharged state, the notice regarding High discharge will appear very quickly, starting in cold weather will be difficult.


Restoring the SOH is a very important argument to register the batter, even if it’s type and capacity is the same as for old battery! Without restoring the SOH it even makes NO SENSE to install new battery!


Old type (before IBS “era”) systems maintained fixed bort voltage (typically 14.0/14.4 V), which ensured charge of lead-acid batter (and, when they were charged, this voltage overcharged them – excess energy was transformed in heat: electrolyte evaporated and the lifetime of battery decreased).

In the situation, when the battery is charged (SOC typically 75 .. 80%), IBS system ensures 0.0 A current in the battery chain, in such way increasing its lifespan. To ensure this 0.0 A mode, onboard voltage is decreased to 12.5 .. 12.9 V. But 0.0 A mode, as we understand, don’t charge the battery (because the current is 0), which means – IBS system has to define SOC correctly! If SOC will be detected faulty (for example, a replaced battery is not registered), the situation, when the partly charged battery is kept in such energetical balance, can appear!

Note: in the overrun mode the bort voltage is increased to 15.0 V, to use “excess” energy much more valuable – to charge the battery.


Another significant topic: E series vehicles, which have IBS system, the battery registration fact (mileage, statistic data of days) are separated from restoring SOC/SOH data. Depending on the car kit (the car has/don’t have Power module, etc.) and way, how the battery is registered (INPA, ISTA D, ISTA P, NCS, tool32 or another tool) very often the situation appears: battery replacement is registered (confirmed by mileage register in INPA menu), but SOC/SOH data are NOT deleted/cleared (are not prepared for new measuring)!


What are the consequences of such a situation?

SOH continues to drop, the battery is used only partly. IBS detects, that the voltage parameters of the battery don’t match SOC and SOH data, functionality is partly turned off and… It’s very possible, that one time you will not be able to start the car, even if you will try to do it immediately after detecting the yellow symbol of the battery in KOMBI. Or, even more simple – IBS will not detect in time (truly) low SOC, will allow the battery to discharge, and you will not be able to start the car.


Below is the entry – how to interpret data, displayed bay INPA, how to make sure, that the registration of battery replacement was successful and – about an experiment of one – two years.


PM field 1

1. mileage (actual, before day, before two days etc.)

2. registered batteries (mileage);

3. driving sessions (minutes), grouping by temperature;

4. driving sessions (hours), grouped by SOC;

5. energy, supplied to the battery; negative balance (actual status, if the balance in negative > 0 Ah);

6. energy, taken from the battery, Ah.

The bottom part of the menu: self-diagnostics data of IBS sensor (POR, POW status).


PM field 2

1. negative energetical balance during the day (if such exists);

2. available start current, relatively;

3. basic data:

a) registered initial capacity, Ah (+1 unit)

b) SOH

c) SOC (actual value)

d) IBS temperature

4. actual SOC and SOC of the end of previous days

5. diagnostic data of IBS peripheral chipset

6. diagnostic data of IBS communication

Note: Battery Kapazitaat in INPA menu displays by one unit higher as registered. Most probably – differences are in the obstacle, that “normal” people start to count from 1, but programmers – from 0.


Most importantly, when registering the battery

After registering the battery (if it’s not performed with ISTA D/P), open PM field 2 with INPA and make sure:

a) SOH = 0 % (old value is deleted, new is not yet calculated);

b) SOC is changed (for example, around 99.7%, if the car has a new battery installed if it’s charged or the car has been with running engine shortly before registering new batter).

In case of a correctly registered battery also fields of input and output energy should be deleted (PM field 1).

If SOC/SOH data are not changed after registering new battery – registration was performed incorrectly!


Note: ISTA D (if no OEM battery code is available) allows to register only battery of existing type and capacity. To register nonOEM battery of another type/capacity, use ISTA P.


My experience with IBS

Two years ago I decided to change the battery. No High discharge indication in the KOMBI appeared, but SOH showed only 30%. The battery was around 7 years old – it has to be replaced prophylactically.


I turned to specialized BMW center (it wasn’t the dealer center, but alternative service, with 20 years of experience) – to entrust the task to the “professionals” seemed to be the right choice.

After installing and coding the battery, it seemed very suspicious, that both SOC and SOH didn’t change.

I decided to not bother but observe the situation. After some time I forgot about observation. Remembered several days ago, when… I had to buy wires for battery, call my friend because I couldn’t start the car.

Yes, the yellow High discharge sign in KOMBI lighted up, but there was not enough energy to start the car with a second try (the first attempt was unsuccessful because the immobilizer worked).


Viewing battery data with INPA after successfully starting the car (after some 15 minutes):

As we can see, in its lifetime, the battery received around +6% of excess energy than used from it (correct parameters), no hour before was closed with 0 .. 40% charge level.


At the same time – SOH has dropped to 15%! Even more interesting – several days ago even 51 Ah negative disbalance appeared (I was sitting in the car and doing my hobby – regulation of the audio) – such high charge in no way matched such low SOH value.

Additionally, during 15 minutes SOC around 85% reached? Even if the battery charge current was several tenths of A, supplied energy don’t reach over 10 Ah. Obviously, the capacity of the battery in IBS “understanding” is close to zero!

Due to unexpected differences of all these data: SOH, in the same time – high real capacity (a low drop of voltage, performing SOC and SOH tests), obviously, was too confusing for IBS system, and its performance was totally paralyzed.

Allowed start current (around 30%) during these two years was not decreased – obviously, for this battery, it was higher than this value (but this parameter, as also SOH, can only decrease). During two years, SOH was evenly decreased from 30% to 15% – even in case of perfect battery IBS calculates natural wear of the battery and adds additional wear every time the car is started (the battery has a high short-term load).


Here, the sample – what happens, if the battery is registered by “specialists”, using INPA. Such nuance, that new battery was 95 Ah, (old – 80 Ah), I’m not even mentioning – un the light of other problems it has no meaning anymore.


Performance of the IBS system after registering the new battery.

Now, just for test, I registered the old battery as new (the same, which was unsuccessfully registered 2 years ago).

As the car was started directly before registering the battery, battery voltage (which IBS uses as one of the parameters to define SOC) was above 12.8 V, which means – the battery is fully charged.

Directly after starting the engine, SOC confirmed value 97.7% (obviously, several % of 100% IBS deducted in the moment of a start as used energy).

SOH is 0% – old value is deleted, the new one is in the calculation process.

In the first 10 minutes, IBS charged the battery to 99% SOC.


After 10 minutes:

As we see, the battery discharge starts.

After 50 minutes negative energy balance of -10 Ah is reached:

All this time IBS was recalculating SOC. After energy balance of -10 Ah, IBS started to charge (full) of the battery, after – next cycle of discharge.


In their documentation, BMW AG mentions, that to define correct SOC, the car has to be put “to sleep” for 2 .. 3 hours. This requirement confirms the requirements, how the charge state of the lead-acid battery has to be determined. After a charge, the battery has to be left in a sleep state for 2 hours, then measure the voltage on its clips. For example, in room temperature (for correct density of electrolyte), 0 .. 100% SOC confirms voltage of 12.2 .. 12.8 V (room temperature 20 +/-5 oC).


On the next day, IBS system performed check of start current (allowed the starter to turn the engine for 4 seconds before allowed to start it), continued the calibration of SOC, when the engine was running and also with a stopped engine. After several cycles, when the car was left locked, but the consumers were working (CCC, etc.), the drop speed of SOC normalized – if in the first times, when the engine was turned on, it was 3 .. 5%/min, then after calibration it decreased to around 1 %/min (which by consumption of around 10 ..15 A means, that IBS has detected the capacity of battery as around 20 .. 30 Ah in this mode, which can correspond around 50 .. 70 Ah in C20 test).


Of course, it’s only your business, how you register and encode (if necessary) the battery. I recommend ISTA D or ISTA P. In another way – you can also become one of the “happy” BMW users, who is not able to start the car on one morning. And even regular replacement of the battery will not help.


BMW AG documents relating IBS: