BYD low-voltage (12V) battery warning: what it means
What the low-voltage power system fault warning light means on BYD EV and DM-i models, and the difference between the 12V battery and the high-voltage battery.
Safety and service note
What this means
BYD models carry two separate batteries: the high-voltage battery that powers the motor and drive systems, and a low-voltage (12V) battery that runs the lights, infotainment, locks and the systems that wake up the rest of the car. The low-voltage power system fault warning light monitors the DC module and the 12V battery when the car is not charging or discharging its main battery.
What causes it
According to the official handbook, if this light turns on while charging, it indicates a fault in the charging system itself. If it turns on while driving, it points to a problem with the DC system or the low-voltage power system more broadly -- not simply an old or discharged 12V battery, though a weak 12V battery is also a common everyday cause of slow starts, dimming lights or infotainment resets even without this specific warning light.
What to do
If this warning light turns on while you are driving, the handbook recommends turning off the A/C and fans, parking safely as soon as possible, and contacting a BYD authorised dealer or service provider. Do not continue driving normally with this light on.
Important
If this warning light turns on while you are driving, the handbook recommends turning off the A/C and fans, parking safely as soon as possible, and contacting a BYD authorised dealer or service provider. Do not continue driving normally with this light on.
Frequently asked questions
Is the 12V battery the same as the main EV battery?
No. The 12V (low-voltage) battery powers lights, locks and infotainment; the separate high-voltage battery powers the motor and drive systems.
What should I do if this light comes on while driving?
Turn off the A/C and fans, park the vehicle safely as soon as possible, and contact a BYD authorised dealer or service provider rather than continuing to drive normally.
Does this mean my 12V battery needs replacing?
Not necessarily -- the light monitors the DC module and low-voltage system as a whole, so the cause could be the battery, the DC-DC converter, or wiring; a technician needs to diagnose which.
Can a weak 12V battery cause other symptoms without this light?
Yes -- slow start-up, dimming lights or infotainment resets can point to a weak 12V battery even before this specific warning light appears.
Is it safe to jump-start a BYD from the 12V battery?
Follow the exact jump-starting procedure in your owner's handbook, since EV and DM-i vehicles have specific precautions around the 12V system; when in doubt, contact BYD roadside assistance.
Does this apply across BYD's range?
Yes -- the low-voltage power system and its fault warning light are described the same way across BYD's current EV and DM-i owner handbooks.
Sources for this guide
This guide is for informational purposes only. Always consult an authorised service centre for safety-critical repairs. AutoTechHelp is not liable for any damage resulting from the use of this information.