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How many volts is a car battery?

Car Battery Voltage

Car Battery Voltage Chart showing the voltages of a car battery at different stages of charge and use

The above chart gives an indication of what the voltage should be at different states of charge and operating conditions. This is intended as a guide only as the voltage reading will be effected by the battery age, technology and temperature.

Fully charged voltage

A fully charged car battery voltage should be 12.6v or above, this is with the engine off. To get a true voltage reading of the cars battery it is important to measure the voltage after the car has been sat for a period with the engine off, preferably overnight, this provides you with the “car battery open circuit voltage” or also know as the “resting voltage”. Measuring the voltage shortly after the engine has been running can give you a higher, misleading, reading.

If the voltage is below 12.6v it indicates that the battery isnt fully charged or has a fault. The voltage doesn’t have to differ much from 12.6v for it to indicate a discharged battery. At 12.2v the battery is in effect 50% discharged.

Voltage when the car is starting

When you start your car, the battery provides the necessary power to the starter motor to turn over the engine. During starting the batteries voltage will decrease for a short time, before going up to the running voltage (see below).

During starting a healthy car battery voltage should be 10v or higher. As mentioned above cold weather needs to be considered as this will decrease the voltage and increase the amount of power to turn over a cold engine.

Voltage when the car is running

The voltage, when the engine is running, should be in the range of 13.5-14.7 volts. When your car is running the cars alternator is charging the battery, this is why you should see a higher voltage. If you’re readings are significantly higher or lower than these then it would indicate a fault with the battery and/or the alternator.

Battery charge and water level

Wet cell car batteries lose water during use and charging, these batteries require regular maintenance. The water level will need periodically checking. For further advice see our guide on filling a car battery with water.

Your car battery is made up of 6 2.1v cells connected in series, combined making a nominal 12.6v. However what voltage your battery should be at any given time is dependent on:

Temperature: The ability of a fully charged, fully functioning car battery to deliver the high current needed to the starter motor is reduced by approximately 40% at freezing point. This is why a weak battery is often discovered in winter when you are about to set off to work on a cold frosty morning!

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As your battery ages and is used, its ability to hold charge will diminish, with a resulting decrease in the voltage.

State of charge:
The voltage of your battery will change as it is charged and discharged. Understanding at what point it is in a charge cycle is important when determining what the voltage should be.

If the cars engine is running or not:
The batteries voltage will be higher when the engine is running.

How to measure car battery voltage.

You can check a car battery voltage with a multimeter or buy a car battery monitor. Both are relatively cheap and easy to use. Check out our guide on checking a car battery with a multimeter.

car battery maintenance

Image: Car Battery Maintenance

Why the voltage of a car battery is important.

Knowing your car batteries voltage is important in understanding the condition of the battery and the likelihood that it could fail.

Your car battery provides your vehicles electrical needs when the engine isn’t running. And importantly it provides the necessary “spark” to get the engine turning over when starting your car. When you start your car the battery provides the high energy (current) needed to the starter motor, which in turn turns over the engine. Once the engine is running the power for your cars electrical systems is provided by the alternator.

The car battery also stabilizes the circuit voltage of the car when the engine is running, protecting the electrical systems from voltage spikes.

Without a fully functioning battery you run the risk of being stranded and unable to start your car.

We advise that you check your car battery a couple of times each year, and in particular towards the end of autumn before winter sets in. It is worth keeping a noted of the voltage readings so you can compare them overtime.

How many amps should I charge my car battery at?

After reading all the electric vehicle primers available online, you might think that you already know everything about the EV charging process — from the different types of chargers to the charging alternatives in the stickiest situations.

But, little is written about how many amps your car battery charger should REALLY be.

This question has more to do with charge rate. It’s important for you to know how long your car’s battery takes to fully charge, so you can plan ahead and not waste your precious time.

Knowing what charger to use is also crucial in determining how long a full charge takes to avoid over charging or overheating.

So, what amp charger for a car battery is right for you? Is it a 2 amp or a 10 amp charger?

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How many amps to charge a car battery?

Knowing how many amps your car battery needs can be a lifesaver for your battery. With too many amps, you risk overheating your battery, which may lead to an explosion. With too few amps, your car battery will take forever to charge!

The safest amp to charge car batteries is from 4 to 7.5 amps. Charging within this range ensures the vehicle battery won’t overcharge, overheat, or be damaged in the process.

Yes, you can safely charge a minimum voltage 12-volt battery with this amp rating, though it will be pretty slow. To increase the charge rate, you’ll need at least 12.9 volts.

You can charge your automobile battery at higher voltages as long as it’s not yet fully charged.

This means that the alternator voltages and the vehicle charger voltages could safely get 15 volts while ensuring the battery won’t get overcharged.

The higher the voltage, the faster a charge cycle is completed.

How many amps do I need to charge a 12v battery?

Deep cycle batteries at 12v cannot handle more than 30 amps of charge current. Fast charging is not recommended for this type of battery, so stick to 10 amps for safety.

Keep in mind that 20 amps is already fast charging, and repeated use of high charging amps may result in bad battery health.

Should I charge my battery at 2-amps or 10-Amps?

The rule of thumb is, lower amps result in a slow charge and higher amps result in higher charging rate.

While safe for your car battery, charging at 2 amps is very slow. You’re highly unlikely to end up with dead batteries, but a battery at 50-amp hours will take 24 hours to be fully charged.

A 10 amp charger can charge a car battery in about 5 hours. There’s a low chance of overheating, but if a short develops, it may cause car batteries to fail.

If a car battery fails, dangerous chemicals could leak. Immediately disconnect the charger from the power source and contact a mechanic.

Can I charge a car battery at 50 amps?

Charging car batteries at 50 amps is already considered fast charging. At 50 amps, you can charge a 50-amp battery in just 1 hour. Use these types of battery chargers in moderation if you want your cars to be safely charged as frequent fast charging may result in decreased battery capacity and poor battery health.

Can you overcharge a battery at 2 amps?

If you leave your car charging continuously, there is still a possibility of overcharging even at a mere 2 amps.

Overcharging your car battery produces excessive gas when electrolytes heat up and both hydrogen and oxygen are produced, eventually leaving you with a completely dead battery.

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To avoid this, take note of your vehicle battery capacity to know how many amp hours it’ll take to fully charge.

Do amps matter when charging a battery?

The amperage matters during a charging process if you want to maintain a healthy battery. Most batteries used in electric cars can handle up to 32 amps.

A 32-amp charger can give your car battery up to 25 miles of range per hour.

An average deep cycle battery has a voltage of 12, but this doesn’t necessarily mean that you can just grab any 12-volt car charger and assume it can be fully charged safely.

If the charger exceeds 10% of the ah rating or the amp-hour capacity of your battery, you run the risk of overheating it. The amps can make or break your car’s battery.

How long does it take to charge a car battery

The more discharged your car’s battery is, the longer it takes for you to get a fully charged battery. As the charge dissipates, you may notice that some of your car’s features won’t work properly. Your car engine might not even start, especially in a cold environment when your battery needs to work double time. This is because there’s not enough power in the batteries to keep them powered-on. Or you don’t have enough cold cranking amps.

When this happens, an indicator light will show up on your dashboard, signaling that your car’s battery needs some charging.

The charging rate will depend on the kind of battery you’re charging and its capacity. To know how long your battery will take to charge, you’ll have to find out the reserve capacity of your battery and your charger’s output charging current.

A battery with 100 amp hours of capacity can be charged by a 10 amp charger in 10 hours.

If you’re charging a flooded lead acid battery, it’ll take more time as it is charged in phases. Voltage is held at a constant during the absorption phase, while current decreases. So, you can’t increase the current and expect faster charging in lead acid batteries.

Tips on how to use your battery charger properly

Investing in a smart charger can save you money in the long run. These chargers communicate with your car, the charging operator, and your utility company through data connections. This optimizes your energy consumption and costs.


Do I need to disconnect my car battery before charging it?

You don’t have to disconnect your car battery before charging as long as you’re using a smart charger that’s microprocessor-controlled. These chargers are designed to prevent any damage to your car.

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What if my charger isn’t working on my dead battery?

If your battery refuses to charge, this is not due to the amperage or your charger. It’s because the charger cannot recognize your battery’s low voltage.

For a charger to recognize a battery that’s hooked up, it must meet the minimum voltage requirement. This voltage varies from manufacturer to manufacturer, but the standard voltage is between 9.5 to 10 volts.

What if my battery won’t charge?

If the charger is not the issue, do some investigation on the EV. Most EVs have a secondary lead acid battery with reserve capacity to support other vehicle features independent of the main battery. This lead acid battery also requires maintenance.

There might also be sulfation and grid corrosion in the battery, which increases internal resistance. Internal resistance opposes the flow of the current, inhibiting power delivery.

How many amps should my battery charger be?

Use a charger with an amp rating that’s about 10% of the total amp hour battery capacity or less. For example, a battery with a rating of 100 amp hours must use a charger rated 10 amps or less. If the battery has 50 amp hours of rating, a 5 amp charger is suitable. Most EV batteries have between 50 amp hours to 70 amp hours of rating, so you’ll want to use a charger with 5 to 7.5 amp.

Can I charge a car battery with a 20 amp charger?

Yes, most EV batteries can handle up to 32 amps, so it’s safe to charge your car battery with a 20 amp charger. It can give you a full battery charge in just 2.5 hours!

Can you charge a car battery with a 15 amp charger?

A 15 amp charger is perfectly fine to be used with a car battery.

Is it better to charge a battery at 2 amps or 10 amps?

If you want a faster battery charge rate, go with the 10 amps. Low charging current at 2 amps can be unreliable, but it won’t hurt if you have two chargers.

Is it safe to charge a car battery at 10 amps?

Yes, it’s safe to charge at 10 amps. You can have a full charge in just 5 hours!

Is it better to charge a car battery at 2 amps or 6 amps?

The general rule of thumb is, the higher the amp, the faster the charging rate. Charging at 6 amps is more reliable than charging at 2 amps.

How many volts is a car battery?



CXC.LOCATION Osprey Heights, Florida

All 12-volt car batteries have a self-discharge rate of some kind. That means if a fully-charged car battery is sitting on your work bench at 12.6 volts in December, if you check back a few months later, it will probably measure a voltage level lower than that. With that being the case, one must acknowledge that if a 12V battery is connected to a car that has electrical accessories using energy, that the battery will discharge even faster.

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The 12-volt battery in this 2001 BMW Z3 is fully-charged at about 12.6-12.8 volts. While this car is 20 years old, it does have some electrical accessories that stay on, even when the car is parked, like the clock in the radio and the seat memory. Over time, those accessories will discharge the battery and we let it sit for a week, to see what the voltage would measure after seven days of not starting the engine. As you can see from the photo, the battery measure 12.46 volts.

That’s not a huge voltage drop and certainly plenty left to start the engine, but if we let it sit for a few more weeks, the voltage would be sure to drop further. People often don’t think of batteries as consumable items with finite lifespans, but they are. Car batteries move closer to their end of use with each day that passes after they are built, whether they get used or not.

Newer cars and trucks that are even more laden with electrical accessories can discharge car batteries even faster. Accessories like car alarms, apps and OnStar that stay on, even when the vehicle is turned off can quickly discharge car batteries in newer vehicles. When was the last time you measured the voltage of your car battery? If it doesn’t measure at least 12.6 volts, it could probably use a maintenance charge.

When any lead-acid battery is discharged below 12.4 volts, sulfation can begin forming in the plates of the battery, which diminishes battery capacity and shortens battery lifespan. That means keeping your battery fully-charged whenever possible will maximize battery performance and lifespan and a great way to do that is with OPTIMA chargers & maintainers. These chargers are microprocessor-controlled and have one-touch functionality. You don’t need to be a mechanic or a gearhead to know how to use one, just look at the pictures on the charger and press the option that matches your battery.

The OPTIMA charger will fully-charge your battery and then keep it properly-maintained without overcharging it, until you are ready to use it again. Connecting the charger is as easy as attaching the black clamp to a ground (like a metal bolt inside the engine compartment and attaching the red clamp to the positive terminal on the battery.

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