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Car Battery Voltage: Know the Basics

Fernando the electronics guy is an electronics engineer. He earned his Bachelor of Science in Electrical Engineering from UC Riverside.

Car battery voltage doesn't look like this. However, it's a nice picture.

Car battery voltage doesn't look like this. However, it's a nice picture.

Car battery voltage is confusing. There are lots of reasons they go bad. Consumers understand small AA batteries. But what about the car battery?

Car batteries are rated at 12 volts. As above, ask yourself the same question. Why is the car battery rated at 12 volts?

1 The Car Battery

All batteries love closed circuits. Voltage is always lower at negative than positive. Voltage passes through the car’s systems. It drops voltage as it’s used up. It drops as much as it needs and carries on to the next.

A battery is a barrage of cells put together. In this case, the car battery is an encasing with 6 cells. Each cell is 2.1 V. Hence why car batteries are 12.6 V.

The car electrical system is designed to need minimum 12 V to function properly. Anything below 12 V and you’ll run into issues. Note not all electrical issues are visible or easy to catch. Most issues come unnoticed.

2 Car Battery Voltage Charge

Now, let’s talk more about the battery charge and its many states and situational requirements.

2.1 Car Battery Voltage Chart


car-battery-voltage

Car batteries generally stay above 12 V during use. According to the chart above, you may use the battery up to 50% of its charge without any consequences.

However, as you approach the yellow and red zones, performance may start to decline rapidly. This is due to the design of the car’s electrical system requiring minimum 12 V.

2.2 Car Battery Voltage Range

Car battery voltage ranges from 0 V to 12.6 V.

The chart above states voltage may be up to 12.7 V. This is due to the fact that each 1.2 V cell isn’t perfectly 1.2 V. They may be 1.21 V, 1.23 V, etc. However so, 12.6 V is a great expectation for a fully charged battery.

  • Of course, the alternator also pitches in a voltage when the car is on.

2.3 Car Battery Voltage When Off

According to the chart above, a properly charged car battery may see a voltage above 12 V.

2.4 Fully Charged Car Battery Voltage

A fully charged car battery will see a voltage of up to 12.8 V.

2.5 Car Battery Voltage at Rest

Let your car rest for about a few hours to a day. You’ll notice one of a few scenarios:

  • Your battery is still above 12 V. The system appears to be functioning properly. The battery is holding a charge. And the system isn’t bleeding voltage.
  • Your battery dipped below 12 V. There’s something wrong. Either the battery is bad, the alternator is bad, or there are parasitic voltage users (think headlights, extra peripherals, etc.).

2.6 Car Battery Voltage to Start

Technically, it is recommended you have at least 11.8 volts to start the car. This means the car battery has fallen to approximately 30% of its storage. This is a low level.

2.7 Car Battery Voltage while running

The alternator is generating anywhere from 13.9 – 14.8 V. This is what the battery sees. The battery is being charged with this voltage. This is what you will see if you read the voltage from the battery while the car is running.

  • Of course, if the alternator is not working properly, you may not see this at all.

3 Car Battery voltage checker

Curious how to check the car battery voltage? You may do so with what’s called a voltmeter. Voltmeters nowadays are packed inside multimeters, an electronic, digital and analog apparatus that is readily available in most stores such as Harbor Freights and Walmart.

3.1 How to Test a Car Battery With a Multimeter

Checking voltage is as easy as:

  1. Turn on your device
  2. Enter “DC Voltage mode”
  3. Positive to positive
  4. Negative to negative

Don’t worry if you got the negative and positive backwards. It doesn’t matter in voltage mode.

Also, don’t worry about getting shocked. You can’t get shocked by checking voltage. It’s almost impossible to do so as the leads aren’t long enough to short circuit between positive and negative battery terminals.

If you find a way to shock yourself you are amazing. Because it’s not going to happen in this mode.

When following the above steps ensure you read your multimeter manual on which mode is DC voltage mode. Also ensure you know which probe is positive and which is negative. This will be useful in the future when you learn to test in other modes.

4 When Your Car Battery Reads 10.8 Volts

Your car battery is nearly dead.

I’d be surprised if you’re able to start the car at this level, as the battery is below 10%.

I would start to ask questions as to why this has happened. Either there is a parasitic drain or some components aren’t working properly.

If you notice this after days of no use, first rule out the electronics. If those aren’t causing this, check your alternator. It may be draining the battery. Yes, some bad alternators do this (they have diodes that sometimes fail and allow current to flow backwards).

5 Car Battery Voltage AC or DC

It’s important to get this right. AC and DC is confusing as it is.

Your house electricity runs off of AC (alternating current). All batteries that are stored in a container of sorts runs off of DC (direct current).

Your alternator creates AC (alternating current). This is passed through rectifier diodes (they convert AC to DC). This is then passed on to the battery (DC to DC).

So, your car battery voltage is in DC.

6 Car Battery Power Pack

There are going to be days on the road where everything seems to go wrong. This is where car battery power packs are useful.

The car battery power pack goes by a lot of names:

  • The car battery jump starter
  • the jump starter
  • the battery jump starter
  • the portable jump starter
  • the portable car battery charger

They are all essentially meant to be the same thing. They will aid you in your quest to get back in the road.

Some scenarios:

  • Can’t start your car? Try the power pack.
  • Left your lights on and now are screwed? Try the power pack.
  • When all else fails … Try the power pack.

I would advise purchasing one and keeping it in your car at all times. You never know when you’re going to need one.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

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