Through 5/31, this Ryobi 40-Volt 16" Lithium-Ion Cordless Walk Behind Battery Push Mower drops from $279 to $179 at HomeDepot.com. Plus shipping is free. That's $100 off the original price and $50 less than we found for comparable models. It features a 40-volt lithium-ion battery, push button start, and has a mulching and bagging system. Sales tax is charged in most states.