@DGL Your 2014 XKR came from the factory with a Battery Management System (BMS) module attached to the negative battery terminal. It is a crucial electronic system that manages and protects the car's battery. The BMS continuously monitors the battery's condition, including voltage, temperature, and current, and protects the battery from overcharging, over-discharging, and other potentially damaging conditions. It's complicated.

I'm just an shade tree mechanic, and my diagnosis is that your problems are caused by that Antigravity Battery Tracker device because it interferes with and prevents the BMS from properly functioning. I would remove that ABT device and pray that it didn't damage your BMS module.

My observation is an example of Occam's Razor, the principle where the simplest, most obvious solution is often the best and most accurate. Your BMS probably was working properly, but you didn't realize it.

For details, see:
How BMS Works - Jaguar Forum

Stuart

 

The Antigravity Battery Tracker(ABT) was installed last week. My strange battery charging behavior has been going on since I bought the car in 2019. The BMS negative cable has been replace. The ABT is connected directly to both battery posts and should not interfere with the BMS.

 

@DGL How do you know that your BMS module wasn't working properly? Did you read this?
How BMS Works - Jaguar Forum

Did a Jaguar dealer or qualified Indy mechanic ever check your BMS module with the ABT attached to the negative battery terminal?

As I previously explained, I suspect that your BMS module was working properly, but you thought it's "strange charging behavior" meant it was defective. It might be defective now that you attached that ABT directly to both battery terminals. Did you remove the BMS module when you attached the ABT device?

 

Since installing the ABT there gas been no change in charging behavior. Everything is the same, expect I see battery charge directly. I also monitor the voltage through the OBD2. The ABT mirrors the OBD2 reading minus about 0.2 volts which makes since.

 

I can't really see how the ABT device can influence the BMS behaviour if it draws just a small parasitic current. I'm guessing it's just a few milliamps (I would measure it to check).
I don't know if I'm going over old ground, but was continuity of the BMS positive connection and fuse checked? This is the thin wire to the positive battery terminal which includes a fusible link inside heat shrink.

 

Quote...
I also monitor the voltage through the OBD2. The ABT mirrors the OBD2 reading minus about 0.2.

Are you saying the ABT reads a slightly higher voltage than OBD? (I initially read it the other way round which would indicate one or other device was inaccurate)

 

The ABT shows a slightly higher voltage. I assume this is because the connection is direct to the battery terminals.

 

A battery maintaining a capacity of merely 12.1 - 12.3 v…. Is a battery that has completed its life.

 

Hi DGL,
Correct: wire resistance means the OBD port receives a lower voltage, 0.2 V less would be typical.

Did the BMS finally kick in with a serious charging voltage of at least 14v?

If not...
After reviewing all your charts I can see the alternator charging voltage is not really exceeding 13v during your driving. I read somewhere that this is the kind of default voltage generated if the BMS LINbus is not connected to the alternator or not connected to the battery positive.



The positive battery connection to the BMS from the small lug includes a fuse inside the sheaf. Check continuity to the BMS 2-pin plug with a multimeter.

If you haven't done already, I'd make physical inspections of the BMS LINbus plug fitted in the alternator (generator) and the 2-pin plug in the BMS unit on the battery negative terminal and also check there is an electrical connection from that 2-pin plug to the battery positive.
Be careful when you check the high current connection to the alternator and disconnect the battery negative terminal before putting a metal spanner on it.

There are also the LINbus connections into the ECU but they would be difficult to check.

Beyond that, maybe get an auto-electrician familiar with smart charging alternators to check it out.

Good luck

 

The battery was going dead because it wasn't getting sufficiently charged. The ctek tells me there is nothing wrong and is showing the green light. However, the Antigravity Battery Tracker is telling a different story saying the battery is only at 23%. The charging voltage shows dropping down when the ctek charging cycle completed.

To me this indicates a bad battery. The voltage should be much higher after a complete charge cycle, but why is the ctek showing a good battery with a green light?

 

Evidently your CTEK is only going by the voltage it sees, not the available amperage.
Someone should have told you that.

 

Could be a wonky CTEK. I have no faith in mine and stopped using it. Different scenario than yours however. Keeps throwing the error light, even though the battery is fine and just needs to be topped up. Opened a case with their support team. They want me to try something for them, but my car is torn apart at the moment, so they’ll have to wait. If they don’t repair or provide a warranty replacement, the thing is going in the dumpster.

 

A CTEK won't tell you if the battery is bad. I have one on my sailboat, the AGM battery is shot, it a provides a few cranking amps for around 20 secs then it's out of steam. The CTEK when reconnected ramps through the cycles to green quickly. It does provide some charge to the battery though.

If it was me I would go back to a regular battery on yer Jag.

 

Before concluding that your battery isn't being charged properly you might want to consider the following;

Jaguar F-Type Battery Management System (BMS) – Theory of Operations

The Jaguar F-Type Battery Management System (BMS) is an intelligent, multi-function control network designed to optimize battery performance, longevity, and integration with modern vehicle systems such as engine stop/start, regenerative charging, and predictive load management. Unlike earlier systems used in the XK X150, the F-Type BMS functions as a dynamic energy ecosystem, balancing real-time charging demands with long-term battery health and emissions compliance.

1. Battery Monitoring and Sensor Network

At the core of the F-Type's BMS is the Intelligent Battery Sensor (IBS), mounted on the negative terminal of the main 12V battery. This LIN or CAN-connected device continuously measures:
- Battery voltage
- Current (inflow and outflow)
- Temperature
- Charge/discharge rate
- Estimated State of Charge (SoC)
- Estimated State of Health (SoH)

The IBS communicates with the Body Control Module (BCM), which then relays data to the Powertrain Control Module (PCM) and Energy Management System (EMS).

2. Adaptive Smart Charging

The F-Type utilizes an advanced alternator control strategy called "smart charging," where the PCM adjusts alternator output in real-time. Key influences include:
- Ambient and battery temperature
- Engine load and RPM
- Electrical accessory demand
- Regenerative braking events

Voltage is actively managed across a range from ~12.6V to ~15.2V. For example, during braking or coasting, the alternator increases output to recover kinetic energy (regen charging), while during acceleration, charging is reduced to minimize engine drag.

3. Start-Stop Integration

The F-Type's BMS is tightly coupled with the vehicle's start-stop system. It continuously evaluates whether sufficient energy exists for safe engine restart:
- SoC must exceed a minimum threshold
- Predicted voltage drop must not compromise safety or comfort
- Accessory load (HVAC, defrost, headlights) must be within limits

If conditions are not met, the system disables start-stop until charging conditions improve.

4. Load Management and Energy Budgeting

During operation, the BMS prioritizes critical systems (engine, steering, brakes) and may temporarily reduce or delay non-critical loads such as:
- Heated seats
- Rear defroster
- In-car entertainment

This predictive budgeting ensures engine restart readiness while maximizing fuel efficiency and driver comfort.

5. Battery Type Calibration and Reset

The F-Type BMS supports multiple battery chemistries:
- Flooded Lead-Acid
- AGM (Absorbed Glass Mat)
- Li-ion (auxiliary applications only)

After battery replacement, recalibration is required via Jaguar's SDD diagnostic tool to:
- Register battery type and capacity
- Reset learned SoC and SoH baselines
- Re-enable full charging logic and smart stop/start functionality

Failure to perform a reset may result in improper charging, shortened battery life, and diagnostic errors.

6. Diagnostic Feedback and Error Handling

The BMS logs diagnostic trouble codes (DTCs) and anomalous conditions, such as:
- U3003-16 (Low Voltage)
- B11DB (Battery SoC Invalid)
- P0562 (System Voltage Low)

These are accessible via OBD-II scanners or Jaguar SDD and are used to trigger load shedding, adjust charge targets, or disable energy-intensive functions.

Conclusion

The Jaguar F-Type BMS is a complex, adaptive system that supports fuel economy, emissions compliance, and electrical system reliability. By dynamically managing charging, prioritizing loads, and integrating with hybrid-style recovery systems, it goes far beyond traditional battery charging circuits. Proper calibration, maintenance, and understanding are essential to maintaining performance and battery life in the F-Type platform.


Prepared on: June 16, 2025

 

DW, since the topic vehicle is XK/R, would you please note the differences between it and the F-Type BMS?

 

My apologies for my earlier post regarding the F-Type.

Here is the Gen 2 Theory of Operations: Jaguar XK/XKR Battery Management System (BMS)

1. Overview

The Battery Management System (BMS) in the Jaguar XK / XKR X150 platform is an integrated electrical control subsystem designed to:
- Maximize battery lifespan
- Ensure sufficient starting power
- Reduce parasitic load during off-state
- Optimize alternator output for fuel efficiency
- Coordinate charging strategy with engine and ambient conditions

The BMS is tightly coupled with the vehicle’s Body Control Module (BCM), Engine Control Module (ECM/PCM), Smart Charging System, and Central Junction Box (CJB).

2. Key Components

- AGM Battery (Absorbent Glass Mat): Designed for deep cycling and higher charge acceptance.
- Intelligent Battery Sensor (IBS): Measures voltage, current, and temperature at the negative terminal.
- Powertrain Control Module (PCM): Commands alternator output and manages charge strategy.
- Smart Alternator (LIN-controlled): Variable output based on real-time PCM commands.
- Fusible Link System: Manages electrical load path and overload protection.
- Sleep/Wake Strategy via CJB: Controls wake/sleep cycles and parasitic load management.

3. Operational Modes

3.1 Engine Off / Key Out:
- BMS enters quiescent mode and progressively shuts down unnecessary modules.
- CJB initiates shutdown delay sequence while monitoring signals.
- IBS logs battery health metrics; may inhibit functions if voltage is low.

3.2 Engine Start:
- Ensures starter motor voltage reserve by shedding non-essential loads.
- May delay crank if SoC is too low.

3.3 Charge Control (Engine Running):
- PCM controls alternator output using LIN bus.
- High-output mode under heavy load or cold start.
- Eco-mode suspends alternator under light load to save fuel.

3.4 Load Management:
- Prioritizes critical systems.
- Load-sheds non-essential systems below 12.3V.

3.5 Sleep Mode:
- Entered after 16–30 minutes of inactivity.
- ECUs in low-power standby; IBS monitors passively.

4. Failure and Diagnostic Behavior

Common DTCs:
- U3003-16 (Battery Voltage – Circuit Voltage Below 11.5 Volt Threshold)
- P0562 (System Voltage Low) Voltage drops below ~11.0 volts for 30–60 seconds with the engine running.
- B1318 (Battery Voltage Low) Voltage falls below ~11.0–11.3 volts (threshold depends slightly on BCM calibration)

These faults can disable non-critical systems and indicate:
- Low battery voltage
- Improper battery type or installation
- Corrosion or bad ground
- IBS failure or LIN bus error

5. Battery Replacement Procedure

To maintain BMS integrity:
1. Use a proper AGM battery (~95Ah, 850CCA).
2. Register battery with IDS/SVDI or compatible tool.
3. Clear all related DTCs.
4. Cycle ignition and validate IBS readings.

6. Enhancements in Later Models

- Post-2010: Improved BMS software supports regenerative charging.
- 2011+: Firmware update improved IBS accuracy and adjusted alternator logic.

Conclusion

The Jaguar XK/XKR BMS is a smart, integrated system balancing reliability, fuel economy, and battery longevity. Proper servicing and battery replacement protocols are critical to avoid operational and diagnostic issues.

7. Voltage Ranges and Diagnostic Alert Thresholds

The Jaguar XK/XKR BMS uses voltage and current readings from the Intelligent Battery Sensor (IBS) to determine battery health, charging needs, and system status. The following ranges and thresholds are typical for diagnostic and operational interpretation:

Normal Operating Voltage Ranges:
- Engine Off (Resting Battery): 12.4 – 12.7V (AGM battery)
- Engine Off (Low SoC or Cold Conditions): 11.8 – 12.3V (still functional, but monitor)
- Engine Running (Alternator Charging): 13.8 – 14.9V (temperature and load dependent)
- Smart Charging Idle State: 12.5 – 13.3V (briefly during eco-mode)

Alert and Warning Levels via OBD II:
- Voltage < 12.0V (with ignition on): May trigger low battery warning (e.g., B1318)
- Voltage < 11.5V (engine off): Classified as low SoC, battery recharge recommended

 

I agree with this. AGM vs flooded have different charging profiles. I've only had modern Land Rovers with BMS fitted with AGM batteries from JLR, never had a BMS issue but symptoms like @DGL were attributed to faulty alternators and faulty batteries. Current AGM (after multiple replacements) is now 3 years old and done over 70K miles with no issues.

I've got a new truck, different make, with a complex BMS and factory fitted with a flooded battery. Enquired with main dealer for AGM equivalent and they said it would not charge correctly as the BMS's only compatible with flooded batteries.