At what point is a 12V battery dead?
Resting fully charged 12-volt batteries are around 12.8-12.9 volts, and flat dead ones are at 12.0 volts, so 12.4 volts on a resting battery means it's about 50% charged.
After three years, it's normally time to install a replacement. After four or five years, most car batteries will be almost completely unreliable. Old car batteries can present a number of safety and reliability issues. Luckily, it's easy to identify if your car's battery is nearing the end of its lifespan.
Connect the multimeter to the positive and negative battery terminals. If you don't have a voltage of around 12.6 volts, you may have a bad battery. Now start the car, and look for a revised voltage over 10. If your voltage drops below 5 when the car is running, it is bad and should be replaced right away.
Average 12V car batteries typically last three to five years, and manufacturers recommend always replacing car batteries once those five years are up.
A typical 12-volt auto battery will have around 12.6 volts when fully charged. It only needs to drop down to around 10.5 volts to be considered fully discharged. If it drops down below that, the battery will become damaged due to excessive sulfation.
- Difficulty Starting the Ignition/Turning Over the Engine. ...
- Dashboard Lights & Lighting Issues. ...
- Electrical Malfunctions. ...
- Poor Performance in Cold Weather. ...
- Strange Odor.
A healthy 12 volt battery should maintain a voltage range from 9.6 - 10.5 volts under the load for a good 30 seconds straight.
Watch the brightness of your headlights. If your headlights dim noticeably as the engine turns over, your battery doesn't pass the load test. The battery should hold enough charge to handle the 10-15 minutes before the engine starts, and once the engine turns over.
A 12V battery contains lead plates which are submerged in sulfuric acid. The battery functions efficiently depending on the immersion of the lead plates, the strength of the acid, and the state of the metal plates. To restore the cells, you need to restore the chemical balance.
When the probes touch the terminals while the car is off and the battery is resting, the multimeter display should show a reading of 12.2 to 12.6 volts (full charge). This voltage range means the battery is in good condition for starting the vehicle.
How do I know my car battery is dying?
Turn on your headlights
It seems almost too easy, but the best way to test the strength of your car battery may be to simply flick on the headlights. If the lights seem dimmer than usual, then it probably means it's time to replace the battery.
Most car batteries that are in good condition will last at least two weeks without needing you to start the car and drive to recharge it. But if you don't intend to drive your car for some time for whatever reason, you should still start it up once a week to recharge the 12-volt battery.
The good news is that the new battery can sit unused for two to four years and still work—as long as it's properly stored and maintained. Your unused car battery can be safely shelved for years if you: Store the battery upright. Keep it in a dry, well-ventilated area.
Bad Battery Symptoms
If the cranking of the engine is sluggish, like your vehicle is harder to start on cold mornings, it starts inconsistently, or there's no sound and interior lights when you try to start, suspect a failing battery, a loose or corroded connection or electrical draw.
- The car is difficult to start.
- Once started, the car doesn't hold a charge for very long.
- Dim or flickering taillights and headlights.
- Dim interior and dashboard lights.
- Random and Spontaneous Illumination of Multiple Warning Lights. ...
- Ignition / Door Locks / Windows / Accessories with a Mind of Their Own. ...
- Auto Start/Stop Failure. ...
- Spontaneous Alarm Activation.
What may drain a car battery when it's off are things such as interior lights, door lights, or even bad relays. While your engine runs, the alternator recharges the battery — which is why you typically don't have to worry about the battery dying while you're blasting the radio on your drive to work!
One of the most obvious ways to tell that your battery is losing punch, and a symptom you might notice without prompting, is a slower engine cranking speed when starting from cold.
At 12.4 volts the battery is considered 75% charged and can still ignite your engine. When the battery voltage lowers to 12.2 volts without the engine running, it is considered a bad battery that may start your engine but is no longer capable of holding a charge.
Stick it to your tongue briefly to know for sure. First inspect the battery for any noticeable signs of degradation, rust, battery acid, etc. If the battery seems reasonably clean, stick it to your tongue. You will feel a slight jolt and metallic taste.
How do you revive a 12v battery that won't charge?
Use Epsom Salt Solution
If the problem is caused by a low electrolyte level, using Epsom salt (magnesium sulfate) to make an electrolyte solution will help revive your car battery. Check out this article on how to check your battery's electrolyte level.
Be warned that adding aspirin will shorten the battery life, as the aspirin will react with the sulfuric acid to form acetic acid. Good for a boost, but bad for the innards of the battery.
Attach a battery trickle charger or a computerized smart charger to your old lead acid battery, and allow charging continuously for about a week to 10 days. The extremely slow charging rates dissolve the de-sulphation that kills the battery, and revives it back to being able to hold a usable charge.
If your voltage is higher than 12.9V, the battery is overcharged. Overcharging can damage a battery, so you'll want to remove some of that excess current.
For a car with a 12V engine, the normal value before starting is between 12.2V and 12.8V, and it should not exceed 14.8V after starting.