How do you start a hybrid car with a dead hybrid battery?

A dead high-voltage (hybrid) battery usually prevents a hybrid from starting, but you can often revive basic systems by jump‑starting the 12‑volt battery. If the high‑voltage pack is truly depleted, professional service or towing is typically required. If only the 12‑volt battery is dead, a jump start can restore power and possibly allow the gas engine to run to recharge the pack.

Hybrid cars rely on two separate power stores: a high‑voltage battery pack that powers the electric drive and a conventional 12‑volt battery that runs the car’s electronics and starter systems. When the high‑voltage battery is exhausted, the vehicle may not start or operate normally, even if the 12‑volt battery is fine. Conversely, a dead 12‑volt battery can prevent the car from booting up the electronics and communications needed to access the hybrid system.

Understanding the hybrid battery system

The high‑voltage battery (often called the HV or hybrid pack) stores energy for the electric motor and is recharged by the engine, the generator, or a charging system in plug‑in hybrids. The 12‑volt battery powers essential systems such as the computer, lights, and infotainment. In many situations, a functioning 12‑volt battery is a prerequisite to enabling the car’s start sequence, but the HV battery’s health ultimately determines whether the vehicle can run under electric power or recharge the pack.

What counts as dead: HV vs. 12V

A dead HV battery means the hybrid pack cannot supply power to the electric motor, and in many models the car will not start or operate beyond minimal electronics. A dead 12‑volt battery prevents the car from booting its computer systems and may also stop the start button or keyless system from functioning. Distinguishing between the two issues guides what you can safely try at the curb.

Preparation: verify what’s dead

Before attempting any manual start, confirm whether the 12‑volt battery or the high‑voltage pack is the issue and assess safety risks. Look for warning lights, dim or flickering headlights, or a rapid clicking sound. If the 12‑V battery shows signs of life, you may attempt a jump start to revive electronics and possibly allow the gas engine to start and recharge the HV battery.

Note that procedures vary by model and some steps involve high‑voltage components. Always consult your owner’s manual or roadside assistance for model‑specific guidance.

• Jumper cables or a portable jump starter


• A donor vehicle with a good 12‑volt battery (or a dedicated boost device)


• Basic knowledge of where the 12‑volt battery is located on your model


• Safety gear such as gloves and eye protection

With the right precautions, a simple 12‑volt jump can restore enough power to proceed with the next steps, but it may not resolve a completely dead HV pack. If the HV battery remains unresponsive after a boost, professional help is advised.

Step-by-step: Jump-start your hybrid’s 12V system

If the 12‑volt system appears functional, you can try a controlled jump start. The exact procedure can vary by model, so use caution and refer to your manual. The following is a general approach that suits many hybrids.

1. Park on a flat surface, set the parking brake, and turn off all accessories.


2. Open the hood and locate the 12‑volt battery and its terminals. If your car's 12‑V battery is not easily accessible, consult the owner’s manual for the correct location.


3. Connect the donor vehicle’s positive cable to the dead battery’s positive terminal, then connect the donor’s negative cable to a clean metal ground on the dead vehicle (engine block or chassis), away from the battery.


4. Connect the donor vehicle’s negative cable to its own negative terminal, then start the donor vehicle and let it run for a couple of minutes.


5. With the donor engine running, go to the hybrid and press the brake, then press the Power button (or start/stop switch) as you normally would to start the vehicle. If the hv battery has enough life, the engine may start and the car will run.


6. If the engine starts, let the vehicle run for several minutes and drive gently to help recharge the HV battery. Then remove the cables in reverse order: negative from the donor, negative from the recipient, positive from the recipient, and finally positive from the donor.

Concluding: A successful 12‑V boost can allow the car to start and run, which may recharge the HV battery. If the HV pack remains depleted, the vehicle may still require service to restore full operation.

What to do if the high‑voltage battery is dead

If the high‑voltage battery is truly depleted, jump‑starting the 12‑volt system alone will not restore full function. In that case, it’s safest to rely on roadside assistance or a dealership for professional assessment and repair. High‑voltage components require specialized training and equipment, and attempting to service them yourself can pose serious injury risks.

1. Do not attempt to drive or perform risky repairs if the HV battery shows signs of failure.


2. Call roadside assistance or contact the vehicle’s dealer for HV‑battery diagnostics and service options.


3. Expect that HV battery replacement or module repair may be necessary, which can be costly and may affect warranty coverage.

For plugin hybrids or newer models, the dealer can perform a HV battery test and advise on whether a recharge, reconditioning, or replacement is required. In some cases, a damaged HV battery is covered by warranty or service plans.

Safety tips and limitations

Always prioritize safety when dealing with hybrid systems. Do not attempt to access or disconnect high‑voltage cables; never touch exposed HV components with bare hands, and keep away from water or damp conditions where high‑voltage parts are exposed. If you are unsure about the procedure or your vehicle’s model has unique steps, contact a trained technician or roadside assistance.

Prevention and maintenance

Regular maintenance of the 12‑volt battery can prevent many roadside frustrations. Keep battery terminals clean, check the charging system, and replace the 12‑V battery according to the manufacturer’s schedule. For hybrids, periodic HV battery diagnostics during routine service can help catch issues before they strand you.

• Have the 12‑volt battery tested at least once a year or during routine maintenance.


• Inspect cables and terminals for corrosion or loose connections.


• Follow the manufacturer’s maintenance intervals for HV battery checks and software updates.

Concluding: Proactive maintenance reduces the chances of a dead battery and keeps hybrid systems operating reliably.

Summary

In a pinch, a living 12‑volt battery can often be used to jump‑start a hybrid and recover basic operation, potentially enabling the gas engine to run and recharge the high‑voltage pack. If the HV battery is truly dead, professional assessment is usually required. Always consult the owner’s manual for model‑specific guidance, follow safe jump‑starting practices, and seek roadside assistance if you are unsure. Regular maintenance of both the 12‑V system and the HV battery helps prevent these situations and keeps hybrids road‑worthy.

Can you still drive a hybrid car if the battery goes dead?

Can You Still Drive a Hybrid Without the Battery? Driving a hybrid without a functional high-voltage battery is generally not recommended. While some hybrids operate on a parallel system where the gasoline engine can function independently, the performance will be significantly compromised.

Can you run a hybrid on gas only?

Yes, a hybrid car can run on gas only, but it will primarily run like a gas-only car and you will lose the electric-only and hybrid efficiency benefits. The gas engine is designed to be the main power source for most driving, with the electric motor and battery assisting to improve fuel economy, especially in city driving or during acceleration. 
This video explains how hybrid electric cars work: 1mHistory of Simple ThingsYouTube · Feb 17, 2025

• How it works: The hybrid system automatically switches between the gas engine, electric motor, or both depending on driving conditions. You can't force it to run purely on gas, but it's the default mode when the battery is low or when you accelerate at higher speeds. 
• Benefits of the gas-only mode: While running on gas only, you will still benefit from the car's regenerative braking system, which helps charge the battery for later use. 
• Potential drawbacks: You will not achieve the full fuel efficiency benefits of a hybrid if you don't allow it to use its electric motor, especially at lower speeds or during stop-and-go traffic. 
• Plug-in hybrids: These cars behave differently. If you don't charge the plug-in hybrid, it will operate in a hybrid mode, similar to a standard hybrid, and rely on gas as the main power source until the battery is charged to a certain point. 

This video explains the different types of hybrid cars: 1mSDA Dan CarsYouTube · Aug 21, 2024

What to do if a hybrid battery dies?

If a hybrid battery dies, first try jump-starting the 12-volt battery as you would a normal car. If the car still won't start, it's likely the high-voltage hybrid battery has failed, and you will need to call a professional for diagnosis and replacement. 
What to do immediately

• Check the 12-volt battery: Most hybrids have a standard 12-volt battery that powers the electronics. If this has died, the car won't start, but you can jump-start it. 
• Locate the jump-start terminal: Your hybrid has specific jump-start points, usually under the hood, and you should consult your owner's manual to find them. Never try to jump-start the high-voltage hybrid battery pack. 
• Jump-start the 12-volt battery: Connect the jumper cables to the designated jump-start terminal on the hybrid and the other vehicle or portable starter, following standard jump-starting procedures. 
• Turn off accessories: Make sure all lights, radio, and the air conditioner are off before trying to start the car. 

This video demonstrates how to jump-start a hybrid vehicle: 56sOrtoTech GarageYouTube · Nov 16, 2024
If the car still won't start

• Call a professional: If jump-starting the 12-volt battery doesn't work, your high-voltage hybrid battery is likely dead and needs a professional diagnosis and replacement. 
• Contact roadside assistance: If you're unable to start the car, it's best to arrange for a tow to a certified hybrid mechanic or dealership. 
• Be prepared for a costly repair: A hybrid battery replacement is an expensive but necessary fix to get the vehicle running again. 

What to know about hybrid batteries

• They are separate: A hybrid has both a high-voltage battery pack and a 12-volt battery, and it is crucial to only jump-start the 12-volt battery. 
• They don't last forever: Hybrid batteries typically last 8 to 10 years, but can fail sooner. 
• Warning signs: Signs of a failing battery include decreased fuel economy, strange engine noises, or fluctuations in the battery's state of charge. Ignoring these signs could leave you stranded. 

Can you jumpstart a hybrid car with a gas car?

The hybrid system is not designed to give a jump start. The dc-dc converter does not have enough amperage to run a conventional starter, and the 12v battery is too small to do it either.