Dewalt 18 batteries are the batteries that power the Dewalt line of power tools. To test the Dewalt batteries, you will need a volt meter. A volt meter measures the volts and watts a battery holds. Using a volt meter will be much faster then if you where to charge and insert the battery into a power tool. You can buy a volt meter at any auto parts or super center for around $20.
Place the volt meter and the Dewalt battery on a clean, dry and flat surface. Turn the volt meter on and allow it the warm up for a minute.
Remove the red and black handled testers from the side of the meter. The testers look like large nails with a handle.
Set the volt meter to volts using the turn knob on the front of it. Touch the black handled tester to the negative output on the battery and the red one to the positive output on the battery. Read the dial on the volt meter to tell if the battery has power.