What Does Ah Mean On A Car Battery (Amp Hours)?
Don’t worry, the car battery specialists are here to give you a super simple answer to the question ‘What Does Ah mean on a car battery?’.
We’ll tell you not only what Ah technically means (the technical answer isn’t what most people actually need to know when they want to buy a car battery), but what it actually means for you to make battery buying decision.
And we’ll let you know how to use the Ah of a given battery to assess whether it’s right for you, and how you should decide between batteries. In other words, how many Amp Hours your battery should be.
Let’s get right to it, then.
Introducing ‘What Does Ah Mean On A Car Battery?’
First we’ll tell you what the technical definition is, then we’ll tell you what you actually want to know – which is what does that mean for me in terms of choosing a car battery.
Ah means Ampere-Hours, sometimes called Amp-Hours, where A stands for Amperes/Amps and H stands for Hours.
A typical car battery is 12 Volts, and car batteries these days tend to have Ah values of around 40 to 100 Ah. Most batteries for most vehicles are in the 40-60Ah range, 60Ah plus is for large vehicles with lots of electronic gizmos to power.
The Ah value refers to how much current the car can produce in one hour.
A 36Ah car battery for example, can, in theory, produce 36A for one hour.
It’s not that that’s what the battery will do, it’s just a measurement which shows the battery capacity. The battery could produce 6A for 6 hours, 1A for 36 hours, 12A for 3 hours, and so on.
In reality, the battery wouldn’t produce quite these numbers, due to heat dissipation across its internal resitance, it would produce a little less.
So, in effect, it’s telling you the capacity of the battery. That is, how much charge the battery can store and how much power it can deliver.
What Ah Battery Do I Need?
That depends on the size of your vehicle, and what electrical consumers you have in your car.
That’s because a car battery is for:
- Starting the engine; and
- Powering electronics
The bigger the engine and the more power-hungry electronics systems, the higher Ah battery you’ll need.
Bigger engine/car = higher Ah needed
Small, light cars with small engines may need as little as 100-150A to start the vehicle. A 40-50Ah battery should be fine for you.
For example, here is the Ford Fiesta battery size. One of the smallest battery sizes is 063, with most batteries falling within this 40-50Ah range (we’ve rated the best batteries for 063 dimensions).
A medium sized car, with medium sized engine, will typically need around 400-600 Amps to start the engine. To be comfortable, you’ll probably want 50-60Ah. If you’re in colder climate, you’ll certainly want to go for the higher Ah if possible. As you may or may not know, batteries don’t like freezing temperatures, and can struggle to get the engine going.
A large-engined, big vehicle may need 600-700A or more to start the engine. If you’re just edging into large territory, you can look at 60-70Ah batteries, but if you’ve really got a big engine and big car, and you have lots of electrical consumers (more on this to follow), you may need a battery as large as 95-100Ah.
More electrical consumers = higher Ah battery needed
If your car has the following:
- Heated windscreens and rear window
- Engine management system
- Safety assistant functions like Lane Assist
- Driving light LEDs
- Electric sun roof
- Power windows
- Central locking
- Interior heater
- Seat heaters
- Headlight cleaning systems
- Anti lock braking system
- Traction control
- Sport mode, or similar engine modes
These functions are taking power out of the battery every time you use them.
If you have more than a few of these, they’re taking a hefty bite out of your battery before we even talk about starting the engine.
In addition, the more often you use the following electrical consumers, the more power you’re consuming.
Radiator fan
If the weather’s hot and you’re stuck in traffic, your radiator fan will be working hard. And it’s a major energy consumer, fully 800 Watts!
Air conditioning
If you use air conditioning often you’re consuming quite a lot of power, taking 500W out of your battery!
Charging electronic devices via cigarette lighter socket
If you often use the cigarette lighter socket to charge phones, tablets etc., then you’ll be consuming around 50W of power.
The more of the above functions you have, or that you use often, the more power your car battery needs, and so the higher Ah battery you need.
How Many Amp Hours Is A Car Battery?
A car battery
So what Ah battery size should I get?
Here’s a rough guide.
| ENGINE SIZE | SIZE OF AH BATTERY NEEDED | ||
| Low Electrical Usage | Medium Electrical Usage | High Electrical Usage | |
| 1.0L | 40Ah | 44Ah | 47Ah |
| 2.0L | 60Ah | 63Ah | 70Ah |
| 3.0L | 80Ah | 85Ah | 90Ah |
| 4.0L + | 95Ah | 100Ah | 105Ah |
To be clear, when we say it’s a rough guide, we do mean that.
If your existing battery is 50Ah and you’ve got a 2.0L engine, does that mean it’s going to conk out any minute? Well, no. Every car is different, and has different power needs.
We’ve provided the above table as a rough guide of recommended approximate Ah sizes you can consider for your size of car and power consumption need.
Bear in mind also, that not all batteries are created equal. A 44Ah Varta battery may provide more starting power than an equivalent 44Ah Lion car battery. (Here are the best car battery brands UK in 2023). And Varta batteries, for example, are likely last longer.
And a 50Ah AGM battery can provide more starting power than the equivalent traditional (normal) lead acid battery.
By the way, before even considering which battery to get, make sure you’re looking at car batteries with the right dimensions for your vehicle. For example, the 096 battery dimensions are: 278L x 175W x 190H (mm).
What About CCA?
Cold Cranking Amps (CCA) should also be taken into account, especially if you live in a climate which gets very cold at times, like us in the UK.
Here’s ‘What Does CCA On A Battery Mean?‘.
Which car battery is right for me?
Here’s how to get the right car battery for you.
Summing Up ‘What Does Ah Mean On A Car Battery?’
So, now you know.
Ah means Ampere Hours, and it refers to the battery capacity and, hence, the power of the battery.
It’s the number if Amps a battery can supply in one hour.
That’s the technical stuff. Most people will want to know how to actually choose the right Ah battery size for their car. So we showed you how the size of your engine means you’ll need a battery with larger Ah value. And larger still if your car has a lot of electrical consumers.
We then gave you an estimate for the size of battery Ah you need, depending on those two factors.
Hopefully it’s answered your question, ‘What does Ah mean on a car battery?’