A quick Google search for the HP62 gives the parts listing
http://www.m-and-d.com/pdfs/ryobi_tool/HP62.pdf and reveals the
correct charger part number is 7224301. A search on the M&D Mowers
website http://www.m-and-d.com/ryobi_tools.html for this part shows
that it is 9V @ 200mA and costs $4.38.

Yeaaaaay! A Google Expert steps forward!
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Al, the usual