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This is a small inexpensive cap, designed to fit on the top of Ryobi One Plus rechargeable batteries, both 18V Lithium ion, and Ni-cad versions. With the addition of two stock metal clips (not included), you can use your battery as a power source for any DIY project. Use one battery, or connect multiple batteries, in parallel or series. The contact clips are available at most online electronic distributors; Keystone part # BK-204, or Tru-Power part # 404B.