Battery Amp Hours Explained (And Other Battery Terms)

Battery Amp Hours Explained

Many readers may be confused by the various terminology associated with the batteries used in cordless electric tools, whether they might be for lawn and garden or other applications.

Often when researching and selecting products, people will come upon the term amp hours, abbreviated as Ah. This can be confusing and intimidating. If you are interested in cordless electric tools of any sort, at some point, you will want battery amp hours explained to you. However, amp hours isn’t the only important thing to understand about the batteries that power your tools.

Why is all of this important? Read on to find out.

Why Should We Care?

I want to avoid confusion first by digging down to the basics. What is anyone really interested in when they are researching and shopping for cordless electric lawn and garden tools? I’m talking apart from things like the quality of the machine, how well it works, how comfortable it is to use.

When it comes to the battery specifically, we care about how much power it will provide, and how long the charge will last for in terms of time spent doing work. What really counts is power and work time in real-world situations.

OK. So What is an Amp Hour Then?

Amp hour is actually itself an abbreviation for ampere hour.

An ampere is the base unit of electric current. Think of electric current like water flowing through a pipe. The more current there is, the more work can be done. The more water flowing through the pipe, the more current there is. The wider the pipe, the more “amps” it has. With electricity, the more electrons flowing through a wire, the more current, or amps, there are.

The amount of current that a machine draws as it operates is measured in amperes, or more commonly, amps.

An amp hour is a number for a battery that means if a machine is drawing that number of amps from the battery, then the charge will be drained in one hour. After one hour of use, the battery will run out and need to be recharged.

Wow. That is Confusing. How About Some Real Examples?

Let’s say you have a cordless electric lawn mower that on average draws 2.5 amps while you’re using it.

  • If you have a 2.5 amp hour battery (normally this would be listed as a 2.5Ah battery), then it will last for approximately one hour of use.
  • If you have a 5.0Ah battery, then it will last for approximately two hours of use for that same lawn mower.
  • A 7.5Ah battery will last about three hours, and so on.

Amp hour means charge time


Note that in the real world the time differences may not be exact. Machines don’t draw a constant amount of current. Many conditions can affect how long the charge on a battery will last. Even the weather can affect battery charge duration.

Generally speaking, the higher the Ah rating on a battery, the longer it will last you.

Also, generally speaking, the higher the Ah rating, the bigger and heavier the battery will be. I typically use a smaller, lighter but lower Ah rated battery for my cordless weed trimmer than I do for my lawn mower. I am carrying my weed trimmer and lighter weight is a great thing. The battery weight doesn’t have a real impact when I’m rolling my lawn mower around.

Wait. What About Voltage?

Batteries don’t just have an amp hour rating. They also have a voltage rating! So what does voltage mean and why should we care about it?

Volts means power

Voltage is a measure mean of power. The unit of voltage is the volt, abbreviated as V. If electricity is similar to water flowing through a pipe, I mentioned that the wider the pipe, the more “amps” you have. Now, if you tilt one end of the pipe higher and higher, you are increasing the power the water can provide, as it pours out of the lower end. This is increasing the “volts”, in our example. Voltage is the pressure with which electrons are driven through the wire. Amps means how many electrons are passing by and volts mean how much pressure they are being driven by.

You Lost Me Again. Why Do We Care About Battery Volts?

Remember that volts means power.

  • A 56 volt (normally this would be listed as a 56V battery) is going to have more power than a 40V battery.
  • Power is important when it comes to how much work a machine can do.
  • Tools that are made to do tough jobs generally need more power.
  • For example, if you want a cordless chainsaw like mine that can cut through large or tough trees, the higher the voltage on the battery it uses, the better your chances of success.

Time Out! I See my Battery Has a Wh Capacity?

No need to panic.

Wh stands for watt hour. A watt is just a measure of electricity that factors in both amps and volts. A watt is defined as current flow of one amp with one volt.

If the above statement is about to give you a headache, have no fear.

For the purposes of lawn and garden tools, you can think of watt hour (Wh) interchangeably with amp hour (Ah). Wh just factors in voltage, where Ah does not.

But what really counts is that the higher the Wh OR the higher the Ah, the longer the charge in the battery will last.

Higher is better for both, but as a reminder the higher the value, often the bigger and heavier the battery will be.

If you’re a bit of a math or physics geek, to get the watt hours, you just multiply the voltage by the amp hours.

  • A 56V, 4Ah battery has 224Wh capacity (56 x 4 = 224).
  • A 40V, 2Ah battery has 80Wh capactiy (40 x 2 = 80).

Don’t worry! There won’t be a test.

Wait. What About What Type of Battery is Used?

You might logically at his point start to wonder about the best type of battery for your needs.

I may delve into this in more detail in the future, but for the purpose of this discussion, when it comes to cordless electric lawn and garden tools, the choice is clear. You want a system that uses lithium-ion batteries.

Lithium-ion batteries may be abbreviated as Li-ion batteries or LIB.

These are the advantages of LIB, and why you will find them in all the best cordless lawn and garden tools.

  1. Lots of power – volts!
  2. High capacity – amp hours!
  3. They can be recharged many, many times.
  4. They have little to no memory effect. Memory effect happens in other types of batteries, so it’s not a concern for us here, although it can be a major problem with certain battery materials.

The best type of battery for your tools

Now You Know What You Need.

Now you have the most important information when it comes to evaluating the power source for your cordless electric lawn and garden tools.

I recommend when you are shopping for a cordless electric lawn and garden tool, you should look at the entire system that the manufacturer offers. Most commonly, there will be an interchangeable battery that can power all the various tools. Manufacturers will offer a variety of batteries that will all fit your tools, but will vary by amp hours.

When it comes to amp hours and volts as well, for lawn and garden tools, higher is better! But do remember that higher amp hours will mean higher battery weight, and of course cost as well. Sometimes materials used in batteries might affect weight. So it is possible to have a 2Ah and a 2.5Ah battery both with the same voltage that weigh the same amount (example).

I wanted to wrap up by mentioning I feel it is very important to have at least one spare battery. I currently have three batteries for my system, and they are two different sizes. I mentioned that I used the smallest one for my weed trimmer. When you have spare batteries, you can always have a backup battery charged and ready to go so you don’t need to wait to continue working.