Symptoms
- Car won't power on or respond to the key/fob at all
- No dash lights, no chimes, nothing happens
- Main battery charge shown in the app might still be high
- Doors may not unlock electronically
Likely causes
- CommonWeak or dead 12V accessory batteryThis small battery powers startup electronics and can die from age or being drained by accessories, separately from the main traction battery.
- CommonCar left unused for a long periodExtended time without driving or charging can allow the 12V battery to slowly drain.
- PossibleFailed 12V-to-main-battery charging systemA fault in the system that keeps the 12V battery topped off from the main battery can cause repeat dead 12V batteries.
What to do
- Check your owner's manual for the EV's specific jump-start or 12V access procedure, since it differs from gas cars and often requires accessing a terminal under the hood or in the trunk.
- If a manual override or physical key is available, use it to access the car per the manual before attempting a jump.
- Have another vehicle or a portable jump-start pack ready and follow the EV-specific jump procedure exactly.
- Once power is restored, let the car sit briefly to allow the 12V battery to receive some charge from the main battery before driving.
- If this has happened more than once, have the 12V battery and its charging circuit tested rather than just jumping it again.
- Avoid guessing at jump points under the hood, since EVs have high-voltage components nearby that should not be touched.
Tools and parts
- Jump-start pack or another vehicle
- Owner's manual for EV-specific jump procedure
12V accessory batterySearch: “12V AGM battery for your EV make, model, and year”
When to call a pro
If the 12V battery dies repeatedly, have a dealer test the battery and its charging system rather than continuing to jump it.
Safety
Use caution
Never touch orange high-voltage cables or components under the hood; only use the manufacturer's specified low-voltage jump points.