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Everything you need to know about power tool batteries

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Power tool batteries in a circle around Badaptor

Buying the right power tool battery can be a tricky business. Navigating all the different battery types, voltages and ampere-hours can be tough, and you need to make sure you get the right battery for your tool. So we’ve decided to cover the basics of power tool batteries, so you can make an informed decision next time you’re looking to buy.

Different battery types

Before we look at battery power and runtime, we first need to know the difference between the types of battery currently on sale.

The most widely-available battery is lithium-ion (Li-ion). This battery technology is used by all the main power tool brands. Lithium-ion batteries have overtaken other battery technologies in recent years thanks to their smaller size, energy efficiency, and slow self-discharge rate. For those that don’t know, self-discharge rate is the speed at which the battery will discharge when it’s not in use.

The only negative of lithium-ion batteries to be aware of is the price. Lithium-ion batteries can be double, or sometimes triple, the cost of other battery systems. Part of this is down to the availability of other types of battery, but also due to lithium’s limited supply and difficulty in extracting it from the earth.

Nickel Metal Hydride (NiMH) batteries are still commonly used as an effective battery system, although they are slowly becoming less popular in the tool world. These batteries are considerably cheaper than lithium-ion batteries and can provide greater current to high-power tools. However, these batteries suffer from a higher rate of self-discharge, pollute the environment upon extraction and disposal, and are susceptible to memory effect.

Memory effect is a condition that means the battery will show as fully charged when it isn’t, causing it to hold less charge than its maximum capacity. For example, if the battery is consistently charged when it’s not completely flat, the battery will remember the point at which it was charged and set that point as its new capacity (almost training the battery to hold less charge).

Older generation tools will typically use Nickel Cadmium batteries also known as NiCds. These were used on the first incarnation of cordless power tools and tended to be bulkier and heavier than more modern batteries. Despite their longer life expectancy, much like NiMHs, NiCds suffer heavily from memory effect and are even more dangerous for the environment. Due to their environmental pollution and difficult disposal, the EU placed a ban on the production and trading of NiCds in September 2006.


Battery voltage determines the overall power/energy of the battery. You’ll find that smaller tools like hand torches or electric screwdrivers, will only require a 12V or smaller battery to run as these tools don’t require a large amount of power to operate. Passing larger voltages through smaller tools can lead to burning out components, causing lasting damage to the tool. Larger and more demanding tools may require anything between 18 and 54V depending on the size and output of the tool. It’s therefore important to check what battery is required when purchasing new tools.

The most common voltages for handheld power tools are 12V or 18V. These voltages provide a good balance between power, cost, and battery size. 12V tools tend to be more DIY oriented as these require less power to function correctly. Most tradespeople will use 18V tools as these provide more overall power.


Capacity in power tools is represented by a number, followed by the letters Ah, which stands for Ampere-hours. This indicates the amount of charge a battery can provide in one hour. For example, a power tool will be able to draw 5 amps continuously for 1 hour with a 5.0 Ah battery.

However, it’s worth noting that this number is only a base estimate as, 99% of the time, the battery will not be under ideal conditions. The actual ampere hours will change based on temperature, battery age, discharge rate and the overall condition of the battery cells.

Although Ah has no correlation to battery power, you will generally find batteries with higher Ah will perform better than batteries with lower Ah. This is due to the way in which the batteries are set up.

Smaller battery packs with lower Ah will generally have a set number of batteries connected in series to form the completed cell. When you connect batteries in series, you add up their combined voltage, but not their Ah. For example, a set of five batteries at 3.6V and 2.0Ah each will add up to 18V, but still 2.0Ah.

To increase a cell’s Ah, sets of batteries connected in series, can be connected to another identical set of batteries in parallel. Batteries connected in parallel add together Ah but not volts. This means that overall, both Ah and volts are being increased by the way the batteries are connected.


When buying new tools, always read product descriptions to make sure you have the correct battery for the tool.

Before you start buying new batteries for your tools, why not see if you can save money with a Badaptor first? With a Badaptor, you can convert your old or underutilised 18V batteries to work with DeWalt, Makita, Milwaukee, or Ryobi tools.

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