The 2008 AL batting champion, who had a .328 average, says his father built a portable device when he was 8-years-old that helped him develop a short, quick, compact swing.
"My father was getting tired of throwing batting practice to my two older brothers and myself, so he built a portable device that allowed us to practice indoors or outdoors by ourselves," Mauer said on his Web site for batting training aids. "The apparatus also helped me improved my hand-eye coordination when using a metal stick bat."
The Twins' catcher, a first-round pick by Minnesota in the 2001 amateur player draft, won the AL batting crown in 2006 with a .347 average.
A back injury could hinder the start of his 2009 season, but no decision has been made about his playing status.