Professional tool reviews for professionals

Maybe you just want to learn more, or to see if your concept of voltage and ampere-hours is correct. Maybe you are new to wireless tools and don't know where to start. Glad you can join the party!

Voltage and ampere-hours are one of the most basic questions raised for cordless tools. It can be confusing. For wired tools, we usually describe the power according to the amperage it draws. This is great when there is an almost unlimited power supply. Most people attribute the number of cordless tools to the idea that voltage equals power and ampere-hour equals running time. Yes... well, kind of... maybe. These two measurements are derived from the actual battery capacity-a term called watt-hours. This is the equation:

Ampere hour x nominal voltage = watt hour

If you look at the label of most batteries, it will tell you the total watt-hours of its capacity. Basically, the bigger the fuel tank (watt-hours), the higher the energy potential you have-it's just a question of how you use it.

If you want to disassemble the battery (please don't do that!), you will find a separate battery unit to store and power the tool. Each battery can provide a certain amount of voltage, which is usually 3.6 volts in the 18650 lithium-ion batteries used. Do I need a 12V battery? String 3 of them into a series. Do you need an 18V battery? Use 5.

If you do math with me, you already know there is a problem. Depending on the amount of charge the battery holds, the voltage inside the battery will vary slightly. They can generate higher voltages than low voltages in a fully charged state. In a fully charged state, a 3.6V battery will actually produce a voltage slightly higher than 4V. Even so, mathematical calculations are not perfect. However, don't lose faith in me. I will explain these exceptions in a future article. Now, let us focus on voltage as power.

If you want more power, just connect another battery in series to the battery. Each time you add a new one, you will increase approximately 4V. In theory, you can do 12V, 16V, 20V, 24V and so on. Fortunately, the tool industry has set up 12V, 18V/20V and 36V platforms for tools, while other combinations are used for outdoor power equipment.

The simple definition of ampere hour is that the battery pack can provide one hour of amperage. Ignoring all other factors (such as temperature and vibration), a 3.0 amp-hour battery will provide you with 3 amps for one hour. A 5.0 amp-hour battery will provide you with 5 amps for one hour. Unlike voltage, this is not a fixed number. You can get higher amperage from the battery and shorten the running time. Jon Bucklew gave an excellent demonstration of this with the Makita 18V LXT brushless angle grinder. You can also consume less current and run longer.

All are linear. Run 2.5 amps with a 5.0 amp-hour battery-you can get 2 hours of runtime. A 3-amp-hour battery consumes 6 amperes of current-now you can only use it for 30 minutes. This is a graph showing how the current drawing affects the running time.

So how do we get these numbers? The operating time of most lithium-ion batteries is about 2000 mAh, or 2.0 amp-hours. When you connect these batteries in series, they still can only produce a total current of 2.0 ampere hours. In a series, the voltage is combined, not ampere-hours.

When you need to increase the number of ampere hours, you can connect the batteries in parallel. The following is an example of a typical 12V battery.

Three 18650 lithium-ion batteries are connected in series.

Each battery carries 3.6 volts and 2.0 ampere hours. Since they are connected in series, we get 10.8 volts (or 12 volts when fully charged), but still only 2.0 ampere hours.

Different electronic devices use the same three batteries, but connect them in parallel. Now they only produce 3.6 volts, but 6.0 ampere hours.

What happens in large-capacity batteries is a combination of series and parallel wiring. First, you connect 5 batteries in series to get the required 18V. Then, wire the other group in the same way. We kept the voltage at 18, but doubled the ampere-hours to 4.0. In theory, we can add another group to get 6.0 ampere hours at 18V.

In the recent best lawn mower article, we noticed that Black & Decker and Craftsman are basically using modified 20V max batteries. They may be. In a 5S2P configuration (5 in series, 2 in parallel = 10 total batteries for 2 groups of 5), the maximum 20V, 5.0 amp-hour batteries and let them all work in series. Now you only need to change the configuration to 10S (10 series), you can get a maximum of 40V, 2.5 amp-hour battery.

A total of 10 batteries are arranged in 2 rows, 5 in series in each row = 20V Max 5Ah battery pack

A total of 10 batteries are arranged in a continuous row of 10 batteries in series = 40V Max 2.5Ah battery pack

Now back to the concept of total watt-hours... No matter how you connect the batteries together, the number of batteries determines the watt-hour of the battery pack. The 40 volt (nominal 36 volt), 2.5 amp-hour Black & Decker battery and its 20 volt (nominal 18 volt), 5.0 amp-hour cousin have a total of 90 watt-hours.

In the real world, things start to get crazy. When you talk about temperature (too hot and cold), vibration, and other environmental conditions, voltage and ampere-hours start to deviate from ideals. However, these conditions are part of life on the site. In some ways, manufacturers set better expectations by simply listing lower ratings that are more representative of the actual work experience (18V nominal instead of 20V maximum).

There are some ways to make better batteries. You can start using the chemicals inside the battery (anode, cathode, electrolyte and other components). The resistance and impedance of each cell are different from other interesting words that most normal people cannot define. This leads to better (or sometimes worse) performance. Suddenly, the same number of batteries that produced 18 volts and 3 ampere hours provided the same voltage, but 4 ampere hours and now 5 ampere hours!

The performance difference between one company and another has a lot to do with the batteries they use. The electronic controls and safety devices they use are also beginning to work. By simply changing the wiring configuration, you can add more power to the battery pack, increase the number of ampere hours, or both. The actual result of the combination can be simplified as higher voltage means more total power and higher ampere hours will result in more total run time.

As manufacturers continue to test different battery and case designs, we will continue to see improvements in the ampere-hour end of the watt-hour equation. For now, it seems that we will continue to see the cordless tool voltage stay at its original position, and OPE is working hard to get into the best state.

On the clock, Kenny deeply explores the practical limitations of various tools and compares the differences. After get off work, his faith and love for his family is his top priority, and you will usually see him in the kitchen, riding a bicycle (he is a triathlon) or taking people out for a day fishing in Tampa Bay.

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When traveling with lithium battery power tools in commercial airlines, the issue of volt-hours is now important. Airlines currently limit lithium batteries to a maximum of 160 volt hours, and they must be installed in equipment—not just spare batteries, they must be carried with you. Lithium batteries are not allowed in checked baggage. For power tools, I suspect that they do not allow the use of impact drivers or similar tools, but the flash may meet the installation conditions. What is the volt-hour of a 4 ampere hour battery? How do you persuade airlines...read more »

Thank you. That's really helpful!

If you look at the 18650 discharge curve, you will find that the 4.0 volt peak voltage of each battery drops to 3.6 volts almost immediately under load. Higher voltages are just advertising hype. Bosch started calling their 12-volt battery 10.8 and changed it to match their competitors. In the European Union, they are still 10.8 volts. From lead-acid to nickel-cadmium batteries, and then to nickel-metal hydride batteries, almost all rechargeable batteries have a charging voltage higher than the nominal voltage, but with the use of voltage drops quickly. The capacity of the battery is also affected by the discharge rate. If you are discharged...read more »

Very good article, and a good explanation of the meaning of Ampere's layman's terms. But it still does not explain how the manufacturer can determine the amount of current, watts, and voltage the tool draws from the battery. Since the battery is depleted, each time the tool is picked up and the button is pressed, the amperage drawn by them is significantly different. So on what digital amperage is the amperage drawn, and which tools are drawing the set amperage so that manufacturers can determine the amperage they print on the package? Different...Read more »

Thank you. I am an elderly (elderly) and a gal, which makes my weight a problem. I have been trying to understand how to get the "maximum" power with the smallest possible weight. It sounds like a bigger Ah will only give me longer use time and more weight, but it will not bring more actual power. Therefore, when I spin a few 2.0 Ah batteries, I will not get any different power intensity, but can only get the same power longer by switching to 4.0 or 6.0 Ah. Am I correct? The weight problem seems to be related to... Read more »

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Professional tool reviews for professionals

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