When cordless power tools initially became mainstream, their batteries were made of nickel cadmium (NiCd). One of their biggest limitations is the so-called memory effect, where batteries could no longer hold the same capacity when they were only partially discharged. You need to fully discharge them before topping them up again. These power tool batteries also lose a certain percentage of charge when you don't use them. Like many other tool brands, DeWalt once offered NiCd-powered tools, specifically its 18V line. The company has since discontinued this range, replacing it with 20V power tools paired with Lithium-ion batteries (Li-ion) instead.

But with the phaseout of DeWalt's NiCd batteries came the introduction of one problem: Can users of still-functional NiCd tools keep their gear? Unfortunately, DeWalt's 18V and 20V power tool batteries aren't completely interchangeable. The good news, though, is that they're one-way compatible, meaning you can actually use the newer DeWalt 20V Li-ion batteries with the older 18V NiCd tools. You can't, however, do the opposite and connect an 18V NiCd battery to a 20V power tool.