Ryobi tools come in two types of batteries: 18v and 36v. These batteries are not the same, and you can't use an 18v battery with a 36v tool or vice versa. If a tool is labelled as 18v, its battery can only be used with other 18v tools, and the same goes for 36v tools. The 36v tools and batteries are mainly meant for gardening equipment and are not compatible with other tools.