Battery Backup And Low-Voltage Disconnect: Toyota/Lexus

Posted on 22 January 2026

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 Toyota/Lexus has to say.

Some Toyota/Lexus models have a backup battery that is part of the Telematics Transceiver (DCM). Toyota refers to the backup battery by different names, including:

Back-up battery (BUB)
Mayday battery
Mobilephone battery

Toyota has low-voltage disconnect considerations for models equipped with a backup battery, which can be found in vehicle-specific service information under: Audio/Visual/Telematics ➤ Cellular Communication ➤ Safety Connect System ➤ Precautions.

Some of these considerations include wait time when disconnecting the low-voltage battery and whether it is a one-time-use part.

Per the 2026 Toyota Land Cruiser Safety Connect System: Precaution document:

"The mobilephone battery is a Lithium-ion type battery and can be charged from the DCM (Telematics Transceiver)."

Per the 2016 Toyota Land Cruiser Safety Connect System: Precaution document:

"When Automatic Collision Notification Has Activated
(a) Perform "ACN CALL END" with the Techstream to terminate ACN (Automatic Collision Notification) with the call center.
(b) The mayday battery (back-up battery) must be replaced."

The backup battery replacement procedures are found in vehicle-specific service information under: Audio/Visual/Telematics ➤ Cellular Communication ➤ Back-Up Battery or Audio/Visual/Telematics ➤ Cellular Communication ➤ Mayday Battery.

In the 2026 Toyota Land Cruiser Back-Up Battery Installation procedure, Toyota states: "When replacing the back-up battery, perform initialization."

Performing necessary initializations after disconnecting the battery and restoring any modified vehicle settings before returning the vehicle to the owner helps ensure a complete, safe, and quality repair.

For additional Toyota/Lexus information, check out the following pages:
Toyota OEM Information
Lexus OEM Information

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Battery Backup And Low-Voltage Disconnect: Toyota/Lexus

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