Words can have more than one meaning. Look at the word gay, for instance. It has two common meanings (attracted exclusively to the same sex and happy) as well as some archaic and obsolete meanings. The same with battery, fluke and many other homonyms.
P.S. neither fluke nor battery are homonyms. Homonyms are being used too broadly to include homographs and homophones. Spelling the same and sounding the same, respectively. Example tear (from the eye) and tear (rip something). Gay is not a homonym.
http://www.cooper.com/alan/homonym_list.html