QX30 Dual Battery

The QX30 uses a dual battery system. The main battery is located at the rear driver side of the engine compartment, and the sub battery is located in the lower dash area on the passenger side.

The main purpose of the sub battery is to prevent any noticeable voltage depletion in the electrical systems when the engine is re-started with the ECO Stop/Start system.

During an engine restart:

The sub battery maintains power to accessory systems, to help prevent loss of electrical system performance, during the short time of an engine restart.
The main battery is isolated to the starting circuit and is used to re-start the engine.

QX30 SUB BATTERY GENERAL INFORMATION

A conventional battery uses acid as the electrolyte, but the sub battery uses a bonded fiber conductive fabric called Absorbent Glass Mat (AGM).

AGM has very low internal resistance.
It is capable of delivering high currents on demand.
It has a relatively long service life, even when deep cycled.

AGM is maintenance-free, provides good electrical reliability and is lighter than the flooded lead acid type.

The sub battery is rated at 170 cold cranking amps.

The 20 hour rate capacity of the sub battery is [V – Ah] 12 -volt – 12 amp hour.

A replacement sub battery, or a replacement main battery, must be of a type and design specific for use with an ECO Stop/Start system.

DIAGRAMS AND EXPLANATION OF DUAL BATTERY SYSTEM

OPERATION DURING ENGINE RE-START

When the ECM calls for engine re-start:

The BCM turns ON the sub battery relay, which connects the sub battery to the on-board electrical system.
Shortly after this, the BCM turns OFF the decoupling relay, which isolates (disconnects) the main battery from the on-board electrical system.
The main battery is used to start the engine.

OPERATION DURING ENGINE RE-START

As soon as the ECM detects an engine speed between 400 to 700 rpm, it terminates the start procedure and transmits the engine running signal to the BCM via CAN communication.

The BCM turns ON the decoupling relay, which connects the main battery to the on-board electrical system.
The BCM turns OFF the sub battery relay, which disconnects the sub battery from the on-board electrical system.

SUB BATTERY RELAY:

Controlled by the BCM.
Turned ON during an ECO Stop/Start system engine restart.
Connects the sub battery to the on-board electrical system during an ECO Stop/Start system engine restart.

DECOUPLING RELAY:

Controlled by the BCM.
Turned OFF during an ECO Stop/Start system engine restart.
Isolates the main battery from the sub battery and the on-board electrical system during an ECO Stop/Start system engine restart.

CURRENT AND TEMPERATURE SENSOR MODULES

Attached to the main battery and sub battery negative terminals.
Monitors battery voltage, current (power usage), and temperature.
Sends sensor information to the BCM.

PYROFUSE

A pyrofuse is integrated to the positive battery cable terminal connected to the main battery. This fuse is opened by the SRS (Supplemental Restraint System) in the event of an air bag deployment. When opened, it cuts the 12 volt electrical power supply to the starter motor and the alternator.

PYROFUSE SERVICE TIPS

Before servicing the pyrofuse:

Always disconnect the negative battery terminal first.
Wait 3 minutes after the negative battery terminal is disconnected.