This is called the “open-cell” or “resting” voltage of the battery. 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.
When charging amperage exceeds the level of the natural absorption rate, the battery may overheat, causing the electrolyte solution to bubble creating flammable hydrogen gas. Hydrogen gas, when combined with oxygen from the air, is highly explosive and can easily be ignited by a spark.
If your battery is reading 0 volts, chances are the battery experienced a short circuit. If the battery cannot reach higher than 10.5 volts when being charged, then the battery has a dead cell. If the battery is fully charged (according to the battery charger) but the voltage is 12.5 or less, the battery is sulfated.
How to Test Sealed Lead Acid Batteries
- Test the battery voltage. Set the voltmeter dial to DC (direct current) volts. Place the voltmeter leads on the positive and negative battery posts.
- Charge the battery. Perform a high-rate charge test.
- Perform a slow charge test. Slow charge the battery for several hours.
A 12V lead-acid battery will not be damaged by overcharge if the voltage is kept low enough to avoid electrolysis, and the charging current is kept below 0.2C (5 times less than the Ah capacity). If it can put out more current than the battery can take then the battery may overheat.
Nothing in the battery world is absolute. The specific gravity of fully charged deep-cycle batteries of the same model can range from 1.270 to 1.305; fully discharged, these batteries may vary between 1.097 and 1.201. Temperature is another variable that alters the specific gravity reading.
Test the alternator to make sure that it can start up the battery. A simple test to check the working of the alternator is by running your car; and then unplugging the positive connection of the battery. If the car stops, then you most likely have a problem with the alternator.
Every car today contains a rechargeable 12-volt battery. The battery light indicates a battery charging problem. If the battery light comes on and stays on while you are driving, the most common cause is a broken alternator belt. Total failure of the alternator is another possibility.
6 Symptoms of a Failing Alternator
- The indicator light.
- Headlights are dim or flickering.
- Other electrical failures.
- Strange noises.
- Car stalls or has difficulty starting.
- Battery dies.
Fully charged automotive batteries should measure at 12.6 volts or above. When the engine is running, this measurement should be 13.7 to 14.7 volts. If you don't have a multimeter to tell you the voltage of your battery, you can do a test of your electrical system by starting the car and turning on the headlights.
If the battery light comes on while the engine is running and the vehicle is being driven, this indicates a problem with the charging system.
- Step 1: Turn off everything that draws power.
- Step 2: Stop the car.
- Step 1: Locate the battery, the fuse box and the alternator.
- Step 2: Inspect the battery.
The cause might be a fouled spark plug, bad plug wire or weak ignition coil. Or, it might be a dirty or dead fuel injector. The problem might be no ignition, fuel or compression. Or, it might be a bad battery, starter, ignition switch or safety circuit, or anti-theft immobilizer system if the engine won't crank.
There are usually two things that cause the battery light to come on after a battery replacement. The most common is a loose connection – perhaps a terminal connector was not tightened sufficiently when the battery was replaced.
Many cell phones have batteries that feature a moisture indicator, which is a sticker that alerts you to water damage. The sticker is normally white, and it turns pink or red when wet. Alternatively, put a new battery in your cell phone. If the phone turns on, your old battery has water damage.
These are some of the most common signs that car battery issues are on the horizon.
- Dashboard Lights. One of the most obvious bad battery signs is a warning light on the car's dashboard.
- Old Battery.
- Slow Start.
- Bulging Battery Case.
- Odd Smell.
- Electrical Issues.
One is marked positive (+), the other negative (-). There are also positive and negative cables in the jumper cable set. The red one is positive (+), the black one is negative (-). Never connect the red cable to the negative battery terminal or a vehicle with a dead battery.
The average cost for a battery test is between $58 and $74. Labor costs are estimated between $58 and $74.
Each battery has two metal terminals. One is marked positive (+), the other negative (-). There are also positive and negative cables in the jumper cable set. The red one is positive (+), the black one is negative (-).
With maintenance-free and gel cell batteries the only way to check the state of charge of the battery is by measuring the voltage. Disconnect the battery to be tested from the vehicle and other batteries. If the battery has just been charged or the vehicle driven, the surface charge needs to be removed before testing.
Yes, wrong car battery size will eventually damage your alternator. As I have mentioned above, whether the battery size is small or large, it will effect damage to your alternator. A small battery will ruin the alternator and make it fail soon enough if you keep using it for short, frequent trips.
Better spark at startup due to the stronger battery. You're not using up all the power available during cranking so the alternator doesn't have to work as hard keeping the car running. A new battery solves the problem.
A car should be able to sit parked for at least a month without the battery dying, unless it's a higher-end car with plenty of power-hungry gadgets and computers, experts say. That reaction keeps happening, but more slowly, when the battery isn't being used. That's why batteries lose their charges as they sit.
But when your engine turns faster, the engine's alternator also turns faster. That way, all of the alternator's power can be directed to recharging the battery. Once the car starts, you CAN rev it up to charge the battery faster, but the best way to do that is to just drive it.
So if you live where it's cold, you need a car battery with more cold cranking amps than you do where its moderate or hot. You should always get at least as many cold cranking amps as the manufacturer recommends, but may want to upgrade if you live where it gets real cold.
If your car does start, let it run for a few minutes to help charge the battery further. Unhook the clamps in the reverse order of how you put them on. Be sure to drive your car for about 30 minutes before stopping again so the battery can continue to charge. Otherwise, you might need another jump start.
