Stairs hit .194 last season with five home runs and 17 RBIs in 99 games with the Phillies.
General manager Jed Hoyer has said this offseason that he wanted to add a left-handed bat for the bench. Stairs will also be available to serve as the Padres' designated hitter in six Interleague road games.
ESPN.com reported recently that Stairs has lost 31 pounds in the offseason in order to get himself ready for Spring Training, going from 230 pounds to about 199 pounds. It's the lightest, Stairs told ESPN.com, that he's been in 15 years.
Stairs is a career .264 hitter with 259 home runs. He's also a career .268 pinch-hitter with 19 home runs.
Corey Brock is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.