It surprises a lot of drivers: their hybrid or electric car has a huge battery, yet it won’t unlock or show “Ready”. In most cases the culprit isn’t the big battery at all. It’s the small 12V one.
Hybrids and EVs still have a 12V battery
The high-voltage battery drives the car, but a normal-looking 12V battery runs the computers, locks, lights and screens. It also “wakes up” the high-voltage system. If the 12V battery is flat, the car can’t switch itself on, even with a full main battery.
Signs the 12V battery is flat
- The car won’t unlock with the key fob
- The dash stays dark, or flickers and shuts down
- The car won’t go into “Ready” mode
- Warning messages appear all at once
Why it goes flat
The 12V battery is usually only topped up while the car is on. Sitting unused for a week or two, short trips, accessories left plugged in, or simply age can all drain it. Many hybrids use a small AGM battery that doesn’t like being run completely flat.
Can you jump start a hybrid or EV?
Usually, yes, using the 12V jump points listed in the owner’s manual. The high-voltage system is never involved.
Orange cables carry high voltage. Never touch or try to work on them. We only work on the 12V system.
Replacing the 12V battery
Hybrid 12V batteries are often in the boot or under a seat, and many need a specific AGM type with a vent tube. Fitting the wrong one can cause problems later. We carry the right batteries and fit them where your car is parked.
