Cordless Grinders

Cordless grinders, especially higher voltage models (18V or higher), provide very similar performance to corded and air grinders, due to modern advancements in battery technology, allowing them to produce high torque and maintain consistent speed under load.

However, they do have limitations in comparison to corded and air grinders, with battery life being the main one. We recommend always carrying a spare battery to reduce any downtime when one battery runs out of power. The other limitation is overheating. An air grinder can grind continuously because it is less likely to overheat, as it has fewer internal components than other grinders, however a cordless grinder may overheat when under continuous and heavy load, such as during deep grinding on thick steel.

We always recommend using an air grinder for non-stop industrial use, however, if the grinding work is in a remote location or where power access is limited, then a cordless grinder will still get the job done.

Yes, but how noticeable the drop-off is depends on the design of the grinder and the battery technology that is used.

In older models, as the voltage drops in the battery, so does the performance of the grinder, which means it will slow down, lose torque and struggle under load. However, modern models, such as those that have a brushless motor, are able to deliver consistent performance for most of the battery cycle and rather than have power that slowly fades, modern tools will cut out to protect the battery from damage and prevent the grinder from performing inefficiently.

Some factors to consider to ensure the battery performs optimally, include -

• Battery capacity (Ah) - When purchasing a cordless grinder, look for higher Ah (amp hour), which indicates the battery can provide longer sustained performance.
• Battery condition - Older batteries naturally lose efficiency because they have completed more charge cycles, which degrades the battery and is normally noticeable after hundreds of cycles.
• Temperature - Extreme temperatures (hot and cold) can reduce power output.
• Workload - Heavy grinding tasks drain power faster than when the tool is used lightly. 

Cordless grinders manage thermal protection and overheating through a combination of electronics, motor design and also some battery safeguards. A cordless grinder can overheat when it is under load for prolonged periods of time, which can degrade the battery and shorten the lifespan of the motor. To protect against this, many cordless grinders have the following features -

• Sensors monitoring grinder performance - If the temperature is too high for the cordless grinder, the system will either reduce power output or temporarily shut the tool down to prevent damage.
• Brushless motor - Modern brushless motors generate less heat than brushed motors, and also provide enhanced control for the operator through enhanced speed control.
• Battery management system - Many modern batteries monitor current draw and temperature at a cell level, so if the battery starts to overheat from either being too overloaded or suffering from poor ventilation, it will cut power until it has cooled down.

We would never recommend using a third-party battery, unless it is specified by the manufacturer that it will work with the cordless grinder. This is because OEM batteries are designed to work with the tool’s electronics, including communication between the battery management system and the grinder, which helps to prevent overheating and provide optimal performance, whereas a third-party battery may not be able to replicate this.

A third-party battery is also not going to be built to the same standard as an OEM battery, which means that lower-quality cells or poor internal construction can result in voltage instability, excessive sag or overheating, especially when the tool is under heavy load, which in extreme cases can increase the risk of fire.

A cordless grinder should always use a battery specified by the manufacturer, for tool compatibility and operator safety, but also to ensure that the warranty stays valid on the grinder.