Mitsubishi Eclipse Cross: PHEV 12V Auxiliary Battery Parasitic Drain and Failure

The Eclipse Cross PHEV maintains a conventional 12V lead-acid auxiliary battery to power the BMS, CAN bus, and ignition systems when the traction battery is isolated. The 12V battery is kept charged by a DC-DC converter from the traction pack, but the system has a known elevated parasitic draw from the telematics and charge management modules that remains active when the car is parked. Battery life is significantly shorter than a conventional ICE vehicle — commonly failing within 2–3 years. A flat 12V will prevent the car from powering on even if the traction battery is fully charged.

• Vehicle fails to power on or shows 'Power System Malfunction' despite traction battery displaying full charge
• Remote key fob range reduces drastically and in-car systems reset, indicating low 12V voltage
• Battery warning light illuminates on consecutive morning starts, often in cold weather when battery capacity is diminished
• 12V battery requires jump-starting within 24–48 hours of sitting idle with no charging activity

1. 1

   Measure 12V battery resting voltage — below 12.4V at rest after 8 hours is marginal; below 12.0V indicates a failing battery.

2. 2

   Perform a parasitic draw test with a clamp meter after all modules have gone to sleep (minimum 30 minutes key-off); Eclipse Cross PHEV draw above 25 mA is excessive.

3. 3

   Confirm the DC-DC converter is functioning by checking 12V rail voltage while the traction battery is active.

Parts involved: 12V battery.

$180 to $600 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Has the car ever failed to start even though the traction battery was charged?”
• “Has the 12V auxiliary battery been replaced, and if so how recently?”
• “Does the car sit unused for more than a week at a time?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.