Hybrid cars rely on two different battery systems – a high voltage hybrid battery that powers the electric motor, and a regular 12 volt battery that powers all of the car’s electronics like the infotainment system, lights, etc. If the 12 volt battery dies, it can cause issues with starting the car and running various electronic systems. The high voltage hybrid battery cannot be used to jump start the 12 volt battery. This article will provide a comprehensive overview of what happens when the 12 volt battery dies in a hybrid car, what warning signs to look out for, how to jump start it properly, and steps to take to prevent the 12 volt battery from dying prematurely.
How does the 12 volt battery work in a hybrid car?
The 12 volt battery in a hybrid car works just like a regular car battery. It is responsible for providing power to all of the vehicle’s electronics like the radio, power locks, interior lights, etc. It also powers the starter to crank the engine when starting the car. The 12 volt battery is charged by the DC-DC converter when the car is on and running off the high voltage hybrid battery. So even when the gas engine is off, the 12 volt battery is constantly being topped up by power from the hybrid battery.
Some key points about the 12 volt battery in a hybrid:
- Powers all electronics like lights, radio, power windows, etc.
- Provides power to the starter motor to start the gas engine
- Charged by the DC-DC converter when the car is on
- Is a regular lead acid 12 volt battery, not related to the hybrid battery
What are the symptoms of a dying 12 volt battery?
There are a few signs that indicate the 12 volt battery in a hybrid car may be dying:
- Difficulty starting the car – If the 12 volt battery is running low, there may not be enough power for the starter motor to crank over the engine. The car will try to turn over but struggles or only clicks.
- Dimming headlights – As the 12 volt battery loses power, it may have trouble supplying consistent voltage to all the electronics. Headlights and interior lights may start to dim or flicker.
- Battery warning light – There will likely be a battery warning light on the dash that illuminates if the charging system senses the 12 volt battery is not maintaining voltage properly.
- Dead power locks or windows – Power locks and windows may stop working if the 12 volt battery loses enough charge. The accessories may work intermittently or not at all.
- Unresponsive infotainment – Low voltage can cause infotainment systems to freeze, reset or be unresponsive. This is one of the first signs of a weak 12 volt battery.
If you experience any combination of these symptoms, have your hybrid’s 12 volt battery tested as soon as possible. Continuing to run on a dying 12 volt battery may cause additional electrical problems.
Can you jump start a hybrid car the same way as a regular car?
Hybrid cars should NOT be jump started the same way you would a normal car with jumper cables. The 12 volt battery can be jump started safely, but hooking up jumper cables to a hybrid battery risks dangerous electrical damage including high voltage electrical shock.
Here is the proper procedure for safely jump starting a hybrid car with a dead 12 volt battery:
- Identify the proper jump start points under the hood. There will be special marked + and – terminals for the 12 volt battery that are isolated from the high voltage system.
- Connect the positive jumper cable to the + terminal and connect the other end to the positive terminal on the good battery/jump pack.
- Connect the negative jumper cable to the – terminal and connect the other end to a ground on the vehicle with the good battery.
- Allow the dead battery to charge for 5-10 minutes before attempting to start the car.
- Once the car has started, allow it to run for 15-20 min to allow the charging system to replenish the 12v battery.
- Carefully remove the jumper cables in reverse order – disconnect the negatives first, then the positives.
Hooking the jumper cables up incorrectly or to the wrong points in the engine bay can cause damage. Only connect to the specific 12 volt jump start terminals. Consult the owner’s manual if you cannot locate the proper connection points.
Why can’t you jump start a hybrid from the hybrid battery?
The high voltage hybrid battery pack provides power to the electric motors in a hybrid car. This battery pack outputs several hundred volts of electricity, unlike the normal 12 volts of a regular car battery. Because of the high voltage, it would be extremely dangerous to try to jump start a 12 volt battery from the hybrid battery.
Dangers include:
- Possibility of dangerous high voltage electrocution from the hybrid battery cables and connectors.
- Can overload or fry the vehicle’s sensitive electrical systems that are only designed to handle 12 volts.
- May trip safety cut-off sensors and render the hybrid system inoperative until repaired.
- Physical damage to the hybrid battery pack or connectors from arcing.
- Voids the hybrid battery and electrical system warranties due to improper access.
Jumper cables are only thick enough to handle the lower amperage of a 12 volt automotive battery safely. Attempting to pass the high amperage of the 300+ volt hybrid battery through standard jumper cables can melt insulation and cause fires or battery explosions. The smart key systems in most hybrids also prevent access to the high voltage battery terminals when the car is off.
What to do if your hybrid won’t start and you can’t jump it?
If your hybrid has a dead 12 volt battery and you either cannot locate the proper jump points or jumping it does not work, you will need to call for professional roadside assistance. Most auto service providers are trained specifically in safely jump starting hybrid vehicles.
Things you should do:
- Make sure your key fob is in the car so it can be put into ready mode for jump starting.
- Pop the hood and make sure the jump point terminals are clean and free of corrosion if present.
- Try holding the start button down for 30-60 seconds to force a recharge of the 12 volt from the hybrid battery.
- If it still won’t start, call for professional assistance. Do not attempt to access or jump from the hybrid battery yourself.
The hybrid battery and charging system are designed to send power to the 12 volt battery when the car is on and prevent drains when off. But long term parasitic drains, extreme temperatures, old age or a charging system fault can still kill the 12 volt battery over time. Call roadside assistance immediately to get your hybrid safely jump started and back on the road.
How can I prevent my hybrid’s 12 volt battery from dying?
While the 12 volt battery dying in a hybrid car is rare, you can take proactive steps to maximize the lifespan of your battery and avoid being stranded:
- Ensure the battery connections are clean and secure. Loose or corroded connections increase resistance which stresses the charging system.
- Fix any pending error codes related to battery charging or voltage output. The hybrid computer will log faults with the charging system.
- Drive longer trips regularly. Short trips do not allow full recharging of the 12 volt battery by the charging system.
- Be diligent about fixing non-hybrid electrical issues quickly like burnt out lights. Parasitic drains run down the battery.
- Replace the 12 volt battery proactively every 3-4 years to prevent failure when you need it most.
- Store in moderate temperatures. Extreme heat or cold reduces battery life and power output.
- Consider a trickle charger or disconnecting the battery if the vehicle will be unused for weeks at a time.
Taking care to maintain the 12 volt battery and electrical system reduces the chances of failure. But having the number of a trusted towing service that can safely jump start hybrids is also a good preventative measure in case your battery does go flat.
Fixing underlying issues if the 12 volt battery keeps dying
If your hybrid’s 12 volt battery seems to die repeatedly, it’s a sign of an underlying electrical issue that needs diagnosis and repair. Some of the potential culprits could be:
- Faulty alternator not properly charging the battery
- Excessive key-off parasitic drain from malfunctioning accessories
- Damaged or missing alternator/charging system belt
- Short circuit in wiring harness draining the battery
- Premature battery failure due to temperature, age or defect
- DC-DC converter malfunction not sending charge to 12 volt system
- Poor battery connections causing charging resistance
- Hybrid/engine computer failure impacting battery charging function
Diagnosing the root cause requires professional diagnosis with a scan tool and multimeter. Things like parasitic drains or specific charging system components at fault require advanced electrical testing. Simply replacing the 12 volt repeatedly will not permanently resolve a fault in the charging and electrical system. The dealership or a hybrid specialist shop is best equipped to get to the bottom of repeated 12 volt battery failures.
Is it safe to disconnect the 12 volt battery in a hybrid car?
Sometimes it’s necessary to disconnect and remove the 12 volt battery in a hybrid, for example when replacing it. However there are a few precautions that should be taken:
- Always disconnect the negative terminal first. When reconnecting, connect the positive first.
- Put the smart key well away from the vehicle if possible. This depowers the high voltage system as a safety precaution.
- Disable the SRS system using dealer scan tool. This disables the airbags to prevent accidental deployment.
- Wait at least 3 minutes after disconnecting the battery before working on electrical components. This allows capacitor discharge in the computers.
- Be aware that systems like power windows may need to be reset after reconnecting the battery.
Follow these steps carefully to avoid personal injury or damage to sensitive electronic components from voltage spikes when disconnecting the battery. Consult your owner’s manual for model-specific procedures. In some cases the dealership may recommend temporarily disconnecting additional battery packs under the rear seat during 12 volt battery replacement as an additional precaution.
Summary of what to do when your hybrid’s 12 volt battery dies
To summarize, here is an overview of what to do if the 12 volt battery in your hybrid car dies:
- Identify if you have a dead 12 volt battery based on symptoms like hard starting and dim lights.
- Locate the marked jump points under the hood and jump from a good battery using proper safety precautions.
- DO NOT attempt to jump from the hybrid battery – use the marked 12 volt battery terminals only.
- If it won’t jump, call for professional hybrid-certified roadside assistance for help.
- Charge the battery fully and have the charging system tested for underlying issues.
- Take preventive steps like cleaning connections and addressing electrical faults to help extend 12 volt battery lifespan.
- Be aware that accessories may need resets and precautions should be taken when disconnecting the 12 volt battery.
While a dead 12v battery is rare in hybrids, knowing how to properly jump start the car and when to seek professional help will get you back on the road safely and prevent expensive damage to the hybrid systems. With some basic preventive care and awareness of the dangers of impromper jumps, your hybrid’s battery will provide many miles of reliable service.
