Tool maintenance is an important part of making sure equipment works efficiently. Cordless impact tools are no exception, and require a fair amount of maintenance to ensure their functionality over the course of many jobs.
Unlike a pneumatic impact wrench, a cordless impact tool should be lubricated daily, the new models should be greased every few months to extend the life and performance of the tool (depending on the usage and application). You can often identify areas that need to be lubricated based on the noise you hear from your tool if you hear a change in noise, its recommended that you remove the hammer case and wipe off the gears, mechanism and anvil, then apply new lubrication to improve the performance of the tool. Specific instructions are provided in the product literature (product information manual).
Also remember to use the correct torque when re-attaching the hammer case.