After years of using your DeWalt tools, it may be necessary to purchase a new battery. Or you just want an extra DeWalt battery to work longer. Choose an 18-volt battery with an amperage of 5.0Ah, for example. You'll have a large battery at your disposal that will continue to work for hours. If it's important to you that your tools remain lighter and you start working less long, an amperage of 2.0Ah is more than sufficient.