Backup Battery And Low-Voltage Disconnect: Mazda

When an accident happens, how will you call for help? Maybe the telematics system, equipped with a backup battery, could automatically do this, even if the main power is cut off. What are the repair considerations, and where can information be found for backup batteries? Let’s see what Mazda has to say.

Some Mazda models are equipped with a backup battery known as a Lead-Acid Battery (SUB) that provides power to the Backup Power Supply Unit. Mazda uses this backup battery to deliver power to:

• Drive Motor Control Module (DMCM)
• PCM
• Door-Electrical Supply Units

Mazda has a Service Precautions document for models equipped with a backup battery, which is found in vehicle-specific body repair manuals (BRM) under: General Information ➤ Service Precautions.

Per the Service Precautions document: "When using an electric welder, remove both the negative and positive terminals of the battery and lead acid battery (sub) to protect electronic components from the overcurrent generated during welding."

The Vehicle Model List document is also found in the General Information area, including a chart detailing model configurations with a backup battery.

The Service Highlights area lists vehicle-specific system and part descriptions. This information helps understand how the PCM interacts with different parts of the vehicle, such as the backup battery.

The Auxiliary Device Power Charging System document is found in vehicle-specific service information under: Service Highlights ➤ EV System ➤ Control System.

Per a 2025 Mazda CX90 PHEV Auxiliary Device Power Charging System document:

• "The Body Control Module (BCM) and other vehicle's electrical devices are activated every time the user opens or closes the door, even when the main power is OFF."
• "Frequent start of vehicle's electrical devices with the main power OFF will consume power of the lead-acid battery and lead to discharge it."
• "If there is a possibility that the lead-acid battery power will drop due to frequent activation of the vehicle's electrical devices when the main power is OFF, the PCM will charge the lead-acid battery with high voltage battery power and prevent it from completely discharging."

This document also outlines the required vehicle conditions to start auxiliary power charging and the typical duration of the charging process. Of the conditions required, Mazda states:

"Not in connected vehicle maintenance mode (MyMazda App connected vehicle)."

To learn more about connected vehicle maintenance mode, check out our App-Based Connected Services Considerations: Mazda article.

Procedures for the backup battery and related parts are located in the following areas of the vehicle-specific workshop manuals under:

• Engine ➤ Charging System
• Body And Accessories ➤ Security And Locks
• Body And Accessories ➤ Power Systems
• Body And Accessories ➤ Control Systems

Remember to disable connected vehicle maintenance mode, restore any modified vehicle settings, and perform required initializations and calibrations before returning the vehicle to its owner.

For additional Mazda information, check out the Mazda OEM Information page.

Additional I-CAR Collision Repair News you may find helpful:

• ADAS, Calibration, And Scanning Article Hotspot
• Backup Battery And Low-Voltage Disconnect
• Collision Information Website Access: Mazda
• Hybrid And Electric Vehicle Article Hotspot
• Step-By-Step: Accessing Mazda Repair Information
• Welding And MIG Brazing Hotspot
• Where Do I Find Other Types Of Information In Mazda?

---

Related I-CAR Courses

Course I-CAR Hybrid And Electric Vehicle Courses