Battery, BMS & charging – Discovery 3 / 4

Battery, BMS & charging – Discovery 3 / 4

11. August 2020 Off By Kenny

Very often, Land Rover Discovery 3 and 4 have been reported to have battery problems.

The Discovery is relatively sensitive to battery voltage and a low battery voltage can even lead to a variety of obstructive error messages (HDC, ABS, suspension, etc.). In addition, the factory installed auxiliary heater often does not work correctly when the battery voltage is low and either does not switch on at all or switches off immediately with a warning message (battery voltage too low).


Batterie Management/Monitoring System

First, some general information about the vehicle: Land Rover Discovery 4 introduced a so-called BMS (actually Battery Monitoring System, but mostly called Battery Management System). This BMS monitors the energy that flows into the battery and the amount of energy that is taken from the battery and intervenes in the charging process of the generator based on this result. One of the functions of the BMS is, for example, to ensure that the battery is not fully charged by the generator (but only up to a maximum of 80%), so that a buffer remains which enables the engine to feed energy back into the battery during overrun. This means that the generator has to be switched on less frequently, which reduces fuel consumption and makes it easier to achieve a better emissions standard.

There are generally two versions of the BMS in Discovery 4. The first is the version that was installed in the vehicle until 2012 and the second is the version from 2012 on, in which a new BMS was installed (part number: LR048601; but you can also get it in our store).



Charging the Battery
The BMS described above makes it necessary that the charger should never be connected to the negative pole of the battery when charging the battery. In this case, the BMS would not notice that the battery is being charged and would therefore assume that the initial situation was completely incorrect. This could result in error messages, poor charging behavior, or difficulties during starting.

For this reason, the negative pole should be avoided when charging the battery, and a ground point should be used instead, see picture. Alternatively, the terminal behind the BMS can be used, which is also located directly on the battery.

If the battery is charged in this way, there is nothing else to consider during the charging process. The BMS registers the incoming current and can adjust its behavior accordingly.


Installation of a new battery (or after charging with negative pole on the battery)

If a completely new battery has been installed in the vehicle, the battery has been removed from the vehicle and charged externally for recharging or the battery has been charged with a directly connected negative terminal, the BMS must be reset. This is the only way to ensure that the vehicle electronics work properly again and that the battery charging procedures run correctly.

A reset can be carried out very easily with a vehicle diagnostic system for Land Rover vehicles. The following instructions apply to the IID Tool from GAP. It is very important that the vehicle battery is fully charged before resetting.

In the IID Tool you move to the category
–> Service/Test
–> BCM Body Control
–> Battery Replacement

The device will then ask you if you really want to continue —> Continue and tell you that the motor must be switched off. Then the diagnostic device resets the BMS and the procedure is finished.

Self-calibration of the BMS

After the BMS is resetted, the BMS performs a self-calibration. To do this, the battery is first charged with maximum charge voltage while the engine is running and then discharged to 75% charge. Discharging can take several days if only short distances are driven. During this time the alternator does not switch on! Only after that the BMS works normally again and charges the battery normally again.

 

Note: The BMS should always be reset at the earliest about 1 hour after the battery has been charged. The voltage of a car battery drops significantly for a period of about 10-60 minutes immediately after recharging – the so-called voltage sack. The causes for this seem to be in the electrochemistry of the battery, but have apparently not yet been researched in every detail. The fact is, if the BMS is reset directly after charging, the BMS assumes an incorrect maximum battery voltage. (Thanks to Hannes F. for the hint)

 

Function test of alternator/generator and general voltage check
The IID tool offers besides the possibility to reset the BMS also other helpful information, which can give you information about the loading behavior of the vehicle.

If you look in the IID tool at the values
–> Live Values
–> BCM Body Control

you will notice that your disco collects and evaluates a lot of information about the loading behaviour.

Among them for example:

  • Average discharge of the battery when the engine is turned off
  • Average charging power with engine started
  • Average discharge of the battery when the ignition is switched on
  • Current current inflow or outflow to the battery
  • Current state of charge of the battery
  • Battery temperature
  • Battery voltage
  • Number of battery changes / BMS resets so far

I have created my own overview page, where I get the data relevant for the battery displayed on one page, so that I always have it quickly at hand.

 

Measuring the functionality of alternator/generator
The generator in the Discovery builds up a voltage of more than 14V (usually 14.2 – 14.5V) when charged correctly. Unfortunately the alternator cannot be switched on manually, so that one must wait for the moment, when the generator is activated by chance, to check if this voltage is reached. I have tried myself to get the system to switch on the generator by activating seat heaters, window heater and air conditioner, but this might not be the best way to do so if the battery is weak in an unfavorable situation ;-).

You should also note that the more modern Discovery engines feed energy back into the battery when the engine is in overrun mode, which means that in overrun mode (you step off the gas and the vehicle continues to roll) voltages of more than 14V can occur.

 

Discovery 4 im Schubbetrieb, die Batterie wird geladen, IID Tool BT

 

So if you want to check if the generator is ok, it helps to activate the graphical display in the IID tool and just drive with constant throttle for a while and let the values be observed (best by a passenger). If the voltage rises to 14.2V or higher during normal driving, you can at least assume that the generator is basically able to reach this voltage.

At the bottom of the picture you can see a recording of the accelerator pedal position and the battery voltage. Whenever I step off the gas, the voltage at the battery goes up (engine in overrun).

DiscoveryParts Batterie Diagnose Land Rover DiscoveryIid Tool with battery voltage display and accelerator pedal position in Discovery 4 SDV6 MJ2012

 

No-load operation, the battery voltage does not drop enough to start the generator despite many consumers being connected

This is what it looks like when the alternator is charging correctly. 14.2V independent of engine thrust or load operation

 

All pictures and diagrams taken with a Discovery 4 SDV6 Mj2012

(In this compilation, a big thanks also goes to our entire WhatsApp group “Disco-Offroader” and also a special thanks to Jürgen and the Blacklandy forum, where great posts on all kinds of problems keep popping up!)

 

My charge voltage does not rise above 13V, what can be the cause?

Normally the battery should be charged with about 14.2V to 14.6V after starting the engine. If this does not happen, this can have different causes, such as
– Corrosion on the positive cable, resulting in increased contact resistance
– Corrosion at the ground connection, resulting in increased contact resistances
– Defect of the BMS
– Wrong reset of the BMW (e.g. reset during the tension bag)
– Generator or charge regulator defective

 

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All information as always to the best of our knowledge and belief, but without guarantee!