In this article, I’ll go over the most common causes of the “Increased battery discharge” warning message. We’ll also have a look at how the system works so you can troubleshoot the problem on your own.
Here’s one more BMW warning message designed to break your daily plans: you get in, start your BMW, and Gong!: Increased Battery Discharge… If you’re like me, your brain immediately starts thinking about what could be wrong.
What Happens When You Get This Warning Message?
Although in most cases you’ll be able to drive just as if nothing happened, sometimes you won’t be able to start the engine. Here are the symptoms connected to the “Increased Battery Discharge” message:
- No start (no crank)
- A slow start (the starter cranks slowly, but the engine starts)
- Electrical consumer power reduction (reduced blower speed, seat heating, etc.)
Before we move on, here’s what “Increased Battery Discharge When Stationary” actually means:
After you park and lock your BMW, all but a few computers will go to sleep. While the electronics sleep, the Intelligent Battery Sensor (IBS) will wake up every minute or so to take a quick reading to determine whether there is enough voltage to restart the engine.
In case the voltage falls too low, the IBS will send a signal to Digital Motor Electronics (DME) with the message “battery voltage is too low.” The DME will then turn off all power-using equipment in the car to save the battery voltage so you can start the engine. This wake-up is intended to be a one-time occurrence.
The message “Increased battery discharge while stationary” basically informs you the DME had to turn off “almost all” electronics to preserve battery voltage.
Now, let’s move on to the most common causes:
- Old (weak) or dead battery
- The battery is not charged enough
- Faulty Intelligent Battery Sensor (IBS)
- Something drained a battery
- Wiring gremlins
1. Old (Weak) or Dead Battery
Obviously, this is the most common cause of the “Increased battery discharge…” warning message. The battery health is low and it can’t hold the voltage for long enough.
When I get a car with this problem, the first thing I’ll do is to check the battery production date. If the battery is more than 10 years old, there’s a 99% percent you found a culprit.
You can find the production date stamped on top of the positive battery terminal.
2. Battery is Not Charged Enough
This is mostly the result of making a lot of short commutes each day. If you drive a car for a mile or two each day, there’s not enough time for the alternator to charge the battery. Just to start the engine, it takes about 200-300A of battery power. On short trips, the alternator won’t have the time to replace this charge. With frequent short trips, your battery will eventually run out.
The same worth for long non-use periods. Besides the batteries’ self-discharge (about 3-5% monthly) there’s also a closed-circuit current consumption to power your BMW’s electronics when the car is parked.
The other reason for not charging the battery enough could be a fault in a charging system, but this fault will usually come with other warning messages.
3 Faulty Intelligent Battery Sensor
The IBS has a microprocessor that can be damaged by moisture (typical for older E-series models). If the IBS is malfunctioning it can wake up the DME over and over for no reason. The DME draws a large amount of power and will quickly drain a battery.
The faulty IBS sensor can also send wrong information about the battery’s state of charge so the alternator will not charge the battery even though it is empty.
In the case of faulty IBS, you can unplug the sensor for a short-term fix. By disconnecting the IBS you interrupt the repeated wake-ups of the DME and preserve battery voltage.
When the IBS is disconnected the DME has no information about the battery state so it sets the alternator output at maximum (about 14.2V), which will consequentially shorten the battery’s life.
4 Something Drained The Battery
Besides “human” errors such as side lights or ignition left on, there are a lot of other things that can drain the BMW battery.
The most common faults are “unwanted” wake-ups by faulty vehicle sensors, actuators, and very rarely ECUs. For example, a faulty shock absorber or door handle electronics can wake up a car’s electronics for no reason and drain the battery.
5 Electrical/Wiring Gremlins
Besides simple and known corroded grounds, power supplies, and broken tailgate wires, sometimes things become complicated.
What I found while chasing these gremlins throughout the years is that most often the faults are caused by aftermarket retrofits. Either they are connected to the CAN bus and interfere with other telegrams, or the installer took the power supply from the wrong terminal.
For example, someone installs a piece of aftermarket electronics, like a trailer hitch module, and powers it from the wrong power terminal. The problem is that now battery management systems can’t manage these aftermarket “consumers.”
The Battery or The IBS?
Let’s say the battery is at 11.7V (discharged) but there’s still enough juice to start the engine. The engine will start and you’ll get a warning message. Now, if the battery is at 11V there’s still enough power to start the engine, but in this case, the DME will prevent the engine start.
To test the theory you can unplug the IBS and try to start the car. Note that without the IBS connected, the warning message will disappear as now DME doesn’t know the state of the battery. So, if you had a no-start condition, and now the engine starts, this can help you to drive away, but you still haven’t isolated the fault.
In such cases, we first want to test the battery.
Battery State of Charge (SoC) and State of Health (SoH)
In most cases, energy diagnosis states that the battery is OK. This is typically an indication of the current State of Charge (SoC), not the State of Health (SoH).
The SoC is defined as the current amount of energy left in the battery (displayed as a percentage). The battery is like a piggy bank. If you keep taking it out and not putting back, you’ll have nothing left.
The SoH is defined as an evaluation of the condition of the battery over a period of time (displayed as a percentage). You cant test the SoH via the ISTA service function.
The DME (engine electronics module) evaluates the state of battery voltage.
How to Test The Battery
This can be done in more than one way. Depending on the tools and equipment available, here are the methods:
- ISTA Test Plan
- Load Tester
ISTA Battery Test
This is possible only on F-Series and some late E-Series. On E-Series BMWs, the power management system and IBS in the vehicle cannot determine if the battery needs to be replaced. This is normal operation for all E-Series vehicles because they do not have the Advanced IBS sensor like the F-Series.
Testing The Battery With Voltmeter
This is the least accurate method, but I also used it to quickly evaluate the condition of the battery. Before the test, you must fully charge the battery and remove the surface charge. To remove the surface charge you can let the battery sit for a few hours or, if you’re in a hurry, just turn the ignition on and a few electrical consumers (headlights, blower, etc.) for a few minutes.
Once the surface charge has been removed you can begin testing.
|State of Charge (SoC)||Voltage (12V)|
To extend the battery service life, your BMW will rarely charge the battery over 80%. So, the first step in troubleshooting is to measure battery voltage at the front jump starter terminals. If the battery voltage shows 12.4–12.7 you know the battery is not the problem.
BMW Battery Monitoring System
The Battery State Information Flow
The DME (Engine Control Unit) monitors the system voltage. When you get the “Increased Battery Discharge” warning message displayed, the DME has sent the telegram via the CAN network that the state of battery charge is below the threshold.
The Instrument Cluster module (KOMBI) picks up the telegram and displays the warning message both in the instrument and iDrive central info display (if available).
Now, here’s where things can go wrong.
The DME module gets the information on the battery state from the IBS sensor, installed on the negative battery terminal. As you may guess, the IBS can also share wrong information. In fact, the faulty IBS sensor can claim that a brand-new battery is dead. If that’s the case, the DME will prevent the engine start.
The IBS communicates via Bit Serial Data (BSD) protocol where it shares the bus network with the alternator, oil level sensor, pre-heating control unit (Diesel) and the DME. So, basically, any of these components can distort the signal.
The BMWs battery management system is not bulletproof. So, if you want, you can drain a battery with lights or radio despite perfectly functioning IBS and power management. And while the radio will turn off by itself here and there, and you’ll have to turn it on again, if you leave hazard flashers on, they’ll work until they milk out the last atom of energy out of your battery.