# Question: How Can You Tell If A 12v Battery Is Good?

## What is a good reading on a 12 volt battery?

A fully charged battery will typically display a voltmeter reading of about 12.6 to 12.8 volts.

If your voltmeter is showing a voltage anywhere between 12.4 and 12.8, that means your battery is in good shape.

Any voltage above 12.9 volts is a good indicator that your battery has excessive voltage..

## Can you overcharge a 12 volt battery?

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.

## Can a completely dead battery be recharged?

It is possible to recharge a dead battery, and depending upon the situation you are in, a dead battery is generally an easy fix, whether you are stuck in your garage and can handle it yourself or you are in the middle of nowhere and need professional, quick, and efficient service in the blink of an eye.

## What is the minimum volts to start a car?

At 12.0 volts there’s much less than a 50% chance that a known good battery will crank the engine over. Remember, 12.0 volts means 0% charge for a known good battery. At 11.0 volts, the chances of the battery actually cranking over the engine are very, very low.

## How do I know if my battery is bad or my alternator?

However, a very simple way to check if the alternator is working is to run the car and disconnect the positive terminal of the battery. If the vehicle stops running, then you probably have a bad alternator. You can also examine your interior and dashboard lights.

## How many volts do you need to jumpstart a car?

12.6 voltsHowever, it must be the same voltage as the car being jumped. Most car batteries are 12.6 volts or above. If you own a more unique vehicle, such as an RV, consult your owner’s manual before getting or giving a jump. Rag or paper towel: This one is optional, but useful if your battery terminals are dirty.

## What is the voltage of a dead 12 volt battery?

12.0 voltsIt’s a good place to start, though. 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.

## How long should a 12 volt battery hold its charge?

Most car batteries which are in good condition will last at least two weeks without needing you to start the car and drive to recharge it, according to the AA. 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 12V battery.

## How long can a car sit before battery goes dead?

two to three monthsLike an automobile, the battery will become fully discharged during the interval from two to three months. If you leave your vehicle with a completely charged car battery parked and do not use the car for 2.5 months, likely, you won’t be able to start the motor of your car.

## Is it safe to leave a car battery charger on overnight?

Even though there is no risk of overcharging with the use of a high quality charger, the battery should not remain connected to the charger for more than 24 hours. A full charge is usually achieved by charging overnight. … Even after a deep discharge, some chargers enable at least partial reconditioning of the battery.

## At what voltage will a car not start?

Even though most cars have 12-volt batteries, 12 V is not enough to jump-start a vehicle. If your measurement device shows this value, the battery is discharged. This may cause sulfation and shorten its lifespan. Therefore, you should always keep your batteries properly charged.

It could be showing a voltage higher than 12 volts and still be bad. If it is bad it will die or drop significantly when put under load. … If the battery measures 12V with no load it is bad or badly in need of a charge. If it reads 10.5V or less when under starter load, you need a new battery.

## Is 11.9 volts enough to start a car?

A flat battery can show 12 volts , but not be good enough to start a car . … 11.9v indicates the battery is completely discharged. Anything under 12.2v means the battery is in a state of discharge, and a healthy battery should show 12.6v in a static state.

## How can you tell if car battery needs replacing?

It’s Time for a New Battery When You NoticeSlow Engine Crank. When you attempt to start the vehicle, the cranking of the engine is sluggish and takes longer than normal to start.Check Engine Light. … Low Battery Fluid Level. … Swelling, Bloating Battery Case. … Battery Leak. … Old Age.

## Can a battery test good but still be bad?

Yes, it could test out okay and still have problems. That is what my batteries did before I replaced them. … Someone finally told me that while batteries can test out okay – they can lose some of their capacity for “cold cranking amps”. I replaced them and all was fine again.

## How do you restore a 12 volt battery?

Mix ¼ Epsom salt with ¾ warm distilled water. You need a quart of this mixture for one cell. Pour the mixture into the cells and shake it around before letting it sit. Connect the charger for the battery and charge for 12 hours.