Found this elsewhere and thought I’d post here for reference.

BATTERY MONITORING SYSTEM
Battery Monitoring System Control Module
Single Battery and Dual Battery System Vehicles
NOTE: The secondary battery on stop/start system vehicles is not fitted with a BMS control module.
On all vehicles a BMS control module is located on the primary battery negative (-) terminal. The module is located on the battery post and is clamped to the post with a bolt and nut.
The primary battery negative ground cable is connected to the BMS control module and is attached to a ground stud on the vehicle body.
The BMS control module is connected into the vehicle wiring harness via a multiplug. The BMS control module receives a 12V power supply direct from the primary battery positive terminal. A LIN bus connection provides communication between the BMS control module, the GWM and the QCCM (Quiescent Current Control Module) for control and monitoring of the battery current drain and state of charge. The BMS control module measures battery current and voltage, which it communicates to the GWM over a LIN bus connection.
The GWM transmits the battery information over the CAN bus to other vehicle systems. Based on the information received from the BMS control module, the GWM and the ECM will control the output from the generator and request the switching off of electrical loads if necessary.
CAUTION: Due to the self-calibration routine, it is recommended that all power supply diagnostic testing is carried out using the Land Rover approved diagnostic system rather than a digital multimeter.
The BMS control module is able to generate DTC's to help diagnose primary and auxiliary battery or generator power supply issues. These DTC's can be read using the Land Rover approved diagnostic system. The Land Rover approved diagnostic system can also be used to implement a primary and auxiliary battery and generator self test routine.
For additional information, refer to: Battery (414-01 Battery, Mounting and Cables, Diagnosis and Testing).
If a fault is detected, the GWM and the ECM will override the BMS control module.
The BMS control module DTC's can be used to help diagnose battery or generator power supply faults. The DTC's are stored in GWM. The Land Rover approved diagnostic system has a process for an automated power supply diagnostic procedure. The procedure provides a menu driven process to locate a fault in a logical sequence. The procedure uses the capability of the BMS control module and generator LIN bus controlled functions to provide current flow information and will detect if the BMS control module or generator are functioning correctly.
BMS Low Battery Warning and Energy Management Messages
The BMS continuously monitors the condition of the primary vehicle battery. If excessive battery discharge occurs, the system will begin to shut down non-essential electrical systems in order to protect the battery.
If the BMS calculates that battery condition is not within set parameters, there are 3 messages that can be displayed, 2 on the touch screen and 1 on the message center. These inform the user that the battery is either at a low level of charge or the engine-off power consumption limit has been exceeded.
Low Battery - Please switch engine on or system will shutdown in 3 minutes: is displayed as a Warning on the touch screen if the engine is not running. This indicates that the battery has fallen below a predefined threshold. As soon as the battery is charged back above this threshold then the message will be removed.
Low Battery - Please start your engine is displayed on the message center if the engine is not running. This indicates that the battery has fallen below a predefined threshold. As soon as the battery is charged back above this threshold then the message will be removed or it can be manually removed by pressing 'OK'.
System will shut down in 3 minutes: is displayed as an Energy management on the touch screen if the engine is not running, and system features are causing excessive battery discharge. After 3 minutes the BMS will begin shutting down vehicle systems. Normal system operation will resume when the engine is started. This is based on a percentage of battery capacity available for the customer to use with the engine off. The percentage can change based upon several factors.
Once triggered, the resetting of this message will not occur until the vehicle is driven for 10 minutes with the engine running (to allow the battery to recoup any lost charge). However, if the engine is run for less than 10 minutes, the message will only be displayed after an additional 5 minutes with the ignition on but engine off.

QUIESCENT CURRENT CONTROL MODULE - ALL VEHICLES
The QCCM is located right rear corner of the luggage compartment. An addition to the Battery Monitoring System, and using signals already transmitted by the BMS control module(s), the QCCM cuts power supply to other non-essential control modules to avoid excessive discharge of the primary battery. The systems supplied via the QCCM are the audio/entertainment systems and the climate control systems.
Some control modules can cause unnecessary battery drain due to the module staying awake after the vehicle electrical system has been shut down. The QCCM in conjunction with the GWM, monitor and control the systems to prevent battery drain.
The system consists of three components:
The BMS control module
The GWM
The QCCM.
The battery monitoring system checks primary battery health by analyzing battery quiescent current, battery current drain or state of charge, and determines if any action is required to protect the primary battery. If action is required this is communicated to the GWM.
The GWM control logic uses this information to determine if action is required to assist primary battery protection. The QCCM receives open and close commands from the GWM and reacts accordingly.
The software that controls the QCCM is contained within the GWM.
The system will be set in transit mode on delivery. Transit mode has no QCCM operation and the relays remain closed. Therefore battery drain could occur and the system will not react to it.
A PDI process requires the system to be put into Normal mode, which enables the quiescent current control module, before handing over to the customer.

The QCCM has a routine to clean the relay contacts if required. This routine is performed using the Land Rover approved diagnostic system and, if unsuccessful, the unit will require replacement.
The module contains a number of fuses which supply and protect the audio/entertainment systems, the climate
systems, the GWM.

GATEWAY MODULE (GWM)
The GWM is attached to a bracket, which is bolted to the passenger side of the cross-car beam, behind the
instrument panel. The GWM contains software to control the following functions:
Determine condition of primary, auxiliary and secondary batteries
Control the output from the generator using load management software
Controls stop/start system using power management to inhibit unnecessary electrical loads
Control the Power Supply Distribution Box to enable the switching of the battery inputs.
The GWM communicates with other system modules on the high speed CAN Powertrain and Chassis, and medium speed CAN Body and Comfort buses.
The GWM communicates with the BMS control module and the power supply distribution box via a LIN bus.

POWER SUPPLY DISTRIBUTION BOX
The Power Supply Distribution Box is located in the right side of the luggage compartment, rearward of the BJB. The power supply distribution box incorporates two banks of MOSFETs, which are activated by the GWM to switch the vehicle loads between the batteries during stop/start on vehicles with stop/start system, and also for charging the secondary or auxiliary battery.
The power supply distribution box receives a battery supply direct from the primary battery to BAT1 terminal and a battery supply from the secondary or auxiliary battery to BAT2 terminal. The power supply distribution box also incorporates a microcontroller, which receives commands from the GWM via a LIN bus connection. The power supply distribution box connects or disconnects either the primary or secondary battery to the vehicle loads according to the GWM commands. In addition, there is a diagnostic connection between the GWM and power supply distribution box, to detect faults with the power supply distribution box.
The MOSFETs in the power supply distribution box have a fail-safe Body Diode mode which will ensure there is always a connection from the primary battery to the vehicle loads in the event of a failure in the power supply distribution box. At least 60A can be supplied to the loads in this mode. The GWM will detect such a failure and will shut down non-essential loads so as not to overload the power supply distribution box.

OPERATION
BATTERY MONITORING SYSTEM AND QUIESCENT CURRENT CONTROL - SINGLE AND DUAL BATTERY SYSTEM VEHICLES
When the ignition is off (power mode 0), the BMS control module records the primary battery state of charge and begins to monitor the battery condition from this point.
If the battery state of charge falls by 7%, the BMS control module will monitor the primary battery for 5 minutes. The BMS control module sends a ‘warning’ message on the LIN bus to the GWM. If after the 5 minute monitoring period, the battery charge has continued to fall or below 50% due to the quiescent drain current being too high, the BMS control module will determine that some control modules are still 'awake'. The BMS control module sends a shutdown message on the LIN bus to the GWM. The GWM sends a CAN bus message on the medium speed CAN Body and Comfort, and high speed CAN Powertrain and Chassis networks to all control modules, requesting them to shutdown.
The BMS control module will monitor the primary battery state of charge for a further 15 minutes and determine if the battery state of charge is still dropping. The BMS control module sends a 'Power Disconnect' signal to the GWM on the LIN bus. The GWM then sends a signal to the QCCM on the LIN bus to open its internal relays. When the QCCM relays are open, the power supply from the primary battery to non-critical control modules is removed. The non-critical control modules are any modules associated with the infotainment system and also the climate control system.
The use of a LIN bus communication ensures that no other control modules are 'woken' during this process. If CAN bus communication was used, all modules on the CAN bus would be woken by the message.
BMS Control Module Self Calibration
Periodically the BMS control module will initiate a self-calibration routine. To self calibrate, the battery monitoring system first charges the battery to its full condition.
NOTE: If the vehicle is only driven for short periods the charging process could take a number of days to
complete.
Once the battery is fully charged, the BMS control module will discharge the battery to approximately 75% of its full state of charge, but never lower than 12.2 V. The time taken to complete this part of the routine is dependent on the electrical load on the vehicle.
When the second part of the routine has been successfully completed, the BMS control module will return the battery to its optimum level of charge. The optimum level of charge will be between 12.6 V and 15 V, depending on battery condition, temperature and loading.
The BMS control module also monitors the primary battery condition with the engine switched off. If a low voltage condition is detected the BMS control module can request the infotainment system is switched off to protect battery voltage.

DUAL BATTERY SYSTEM - STOP/START SYSTEM VEHICLES ONLY
The dual battery system prevents electrical loads on the vehicle being subjected to low voltage levels during an ECO (stop/start system) engine start. Low voltage can occur due to the power demand of the TSS (Tandem Solenoid Starter) motor and could result in degraded performance of components and/or system control modules. The GWM contains the software to control the dual battery system and electrical load management system to ensure that ECO engine starts do not affect other vehicle systems.
The dual battery system isolates all power supply sensitive electrical components which may be affected by low voltage from the primary battery due TSS motor operation, and supplies them with power from the secondary battery when an engine start is in progress.
The power supply distribution box contains two banks of MOSFETs, which operate to change the power supply into two separate circuits when an ECO engine start is required. Sensitive electrical components are supplied from the secondary battery. The primary battery power is used exclusively to supply the starter motor and maintain essential power loads to the engine management system required for engine starting. The power supply distribution box operates according to commands from the GWM over the LIN bus. Christian.


Current Cars
2011 Range Rover Vogue SE
2020 BMW M4 Competition
2019 BMW X4

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