Car Battery Voltage Chart UK (12V)
In this article we’ll present you with the definitive 12V car battery voltage chart, UK.
We’ll also clearly and concisely describe exactly how you can interpret these battery voltages.
In other words, we’ll show you what the voltage actually means for your 12V battery, and if there’s any need to be concerned.
We’ll deal with both the resting voltage (AKA open circuit voltage) of the battery, and the voltage during the charging process.
Introducing the 12V Car Battery Voltage Chart
Without further ado, then, here is the 12V lead-acid battery voltage chart.
Very Important: The following table shows the resting voltages of the battery.
That means they show the voltage measured when the battery is not in use ie. the car is not being charged, or started or driven.
A true resting voltage also requires you to measure when the battery has not been used (by being charged or driven) for at least a few hours.
If you measure the voltage of a battery immediately after use, this is not a resting voltage.
Also important: this chart is for Flooded lead-acid batteries (which is what the vast majority of cars use – the main other common types in the UK are EFB and AGM).
| Charging Status % | Car Battery Resting Voltage |
|---|---|
| 100% (Fully charged) | 12.6-12.7V |
| 90% | 12.5V |
| 80% | 12.4V |
| 70% | 12.3V |
| 60% | 12.2V |
| 50% | 12.0V |
| 40% | 11.9V |
| 30% | 11.8V |
| 20% | 11.7V |
| 10% | 11.6V |
How to use this 12V car battery voltage table?
So we’ve given you the table, but how can you interpret this to make a proper analysis of the state of your car battery?
Your battery is going to be fully charged at a resting voltage of around 12-6 to 12.7V. This varies depending on the age and condition of the battery. It also changes according to the weather; a 12V car battery’s voltage falls in low temperatures.
As a result, then, if you measure could be that your vehicle battery’s voltage is 12.5V and yet it’s actually fully charged.
The same applies if your battery has been around the block a few times ie. it’s getting old. Or if it’s not been treated with plentiful charge often enough and it’s suffering from sulfation. In that case the maximum fully charged voltage of the battery could be 12.5V or less.
You may be thinking, then, how can I ever know what the fully charged voltage actually is?
Well, here’s how…
How can you find out what your battery’s voltage is when it’s fully charged?
Just follow these simple steps:
Step 1:
Charge it overnight, or take it for a good long trip on the motorway. This way, you know it’s fully charged
Step 2:
Let the battery rest for at least 6-8 hours – overnight would be ideal.
Step 3:
Measure the battery voltage using a voltmeter or ideally a car battery tester (they’re much more accurate). The resulting voltage you measure is the voltage of your battery when it’s fully charged.
What if my fully charged resting battery voltage is less than 12.6-12.7V?
Firstly, make sure you’ve followed the steps above to find out your vehicle’s resting voltage when fully charged. What does it mean if that voltage is below 12.6 to 12.7 Volts?
This lower voltage indicates either the battery is not in tip-top condition or the temperature outside is low (here’s how cold weather affects batteries).
Here’s a very rough table showing what charge percentages may apply if your fully charged voltage is 12.5 volts.
| Charging Status % – Older Battery/Cold Weather | Car Battery Resting Voltage |
|---|---|
| 100% (Fully charged) | 12.5V |
| 90% | 12.4V |
| 80% | 12.3V |
| 70% | 12.2V |
| 60% | 12.1V |
| 50% | 11.9V |
| 40% | 11.8V |
| 30% | 11.7V |
| 20% | 11.6V |
| 10% | 11.5V |
What voltage is needed to be able to start my car?
Normally, at least 11.8V is required, but if it’s cold, or some of the vehicle components are not in the best condition, this may not be a high enough voltage.
12V Car Battery Voltage Table – When Charging/Starting/Running The Car
Let’s now check out what various battery voltages mean when the battery is in use ie. when you are starting or running the car, or when you’re charging the battery using car battery charger (here are the UK’s best car battery chargers).
| Charging Voltage | 14.0-14.8V |
| Vehicle Running | 13.4-14.7V |
| Starting Voltage | 10.0V |
If your 12V battery charger shows a charging voltage you can expect it to be around 14.0 to 14.8V for a typical Flooded lead-acid battery.
If you have a 12V battery monitor (the best 12V Bluetooth battery monitor are the BM6, followed by the BM2), you may be able to see the voltage of the battery while you drive, or while the engine’s running. In that case, it’ll typically move up and down between 13.4 volts and 14.7 volts, varying depending on whether your foot is on the accelerator pedal or not.
The starting voltage of 10.0V is something you’ll typically only see on a battery monitor which logs a voltage graph over time. The voltage graph will dip sharply down to 10V, then rapidly spike up to the typical running voltage range, as mentioned immediately above, of 13.4-14.7V.
Do your resting voltage results indicate the health of the battery?
Not as such. They just show how much charge is in the battery at that specific moment.
To get a measure of battery health, you can use a 12V car battery tester, and you’ll get a reading for CCA (Cold Cranking Amps). This is the true measure of the health of the battery. Most testers will then compare the current CCA of the battery with the rated CCA (the CCA written on the battery, the amount it’s rated for when the battery was new), to give you a resulting battery health percentage.
Battery voltage readings, as described in this article, still have value, though. If the voltage of the battery when fully charged is below 12.6 to 12.7V, and the weather is not too cold, it’s a sign that the battery is not in the best of health.
If you regularly measure your battery voltage, and it’s consistently below fully charged, it could be a sign that you’re not driving the vehicle long enough to charge the battery completely. Batteries want long journeys; lots of short journeys may never give the battery the full charge it needs. FYI, here’s how long batteries last when you don’t drive them.
If you are driving long distances, or you use a battery charger, and you still find that voltage is often below full charge, it may be that the battery is in poor health. But for a more accurate analysis, a car battery charger is necessary.
What else can you do apart from monitoring battery health? You can get a jump starter (the top model on the UK market is the Topdon Jump Surge 3000 jump starter, followed by the NOCO GBX155 booster). These days, with the advent of LiFePO4, the leading products are small, light and super safe.
Or check out the battery desulfators that actually work -they remove and prevent the build up of sulfation (lead sulfate on the battery plates), the main reason for battery deterioration. Check out this F16 Pulse King UK review to see the top performing desulfator in this field.
Car Battery Voltage Chart UK Summary
We gave you the definitive Car Battery Voltage Chart for cars in the UK, in 2023.
We talked about what these voltages actually mean, and how you can interpret the battery voltages you measure.
We noted that 12.6-12.7 Volts is the normally voltage for a fully charged battery, and showed which voltages correspond to which approximate charge % level.
Be aware with analysing voltage – it doesn’t show the health of the battery per se, it just shows how much charge is in the battery at the moment you measure. But analysing voltages in different situations, and over time, can provide valuable information.
Speaking of valuable information, we hope this article was just that for you!