The CPSC has announced the recall of certain 18 V Lithium battery packs:
http://www.cpsc.gov/en/Recalls/2013/One-World-Technologies-Recalls-Ryobi-Cordless-Tool-Battery-Pack/
http://www.cpsc.gov/en/Recalls/2013/One-World-Technologies-Recalls-Ryobi-Cordless-Tool-Battery-Pack/