The negotiations parried back and forth for weeks in early 2010, encompassing virtually every detail of Joe Mauer’s career. His lionization in his hometown. His status as an All-Star, and his allure to high-payroll contenders. His burgeoning power, Gold Glove defense and injury history.

Every factor that the Twins and Mauer’s representatives could think of was discussed, projected and appraised before an agreement was reached. Every factor but one.

“I don’t think there was ever any expectation on either side,” Mauer’s agent, Ron Shapiro, said, “that Joe would be anything but a catcher.”

It was simple supply and demand: Catchers who can hit are scarce. Batting champions who can throw out baserunners and handle a pitching staff, they’re unicorns. Joe Mauer wasn’t the best of his class, he was the only member, a singular talent that Shapiro believed could be worth $30 million a year on the open market.

At $184 million over eight years, the terms the two sides finally agreed upon, the Twins were purchasing, practically into perpetuity, an asset that no other team possessed.

An asset that lasted under that contract, as it turned out, for only 192 games.

“Joe was the best catcher in the game. Of course you’d hope he would be able to stay back there his entire career,” said General Manager Terry Ryan, who was an adviser to former GM Bill Smith during Mauer’s negotiations. “But things happen that you can’t anticipate. So you adapt.”

A concussion is what happened. A full-time move to first base that Mauer had a difficult time embracing is how the Twins will adapt, beginning next week in Fort Myers. And the truth is, the team is better prepared for the transition than it might seem, because Mauer hasn’t been healthy enough to be the Twins’ regular catcher for years.

“You’d like to have your catcher catch about 130 games a year, the top-of-the-line guys like the Yadier Molinas of the world,” Ryan said, referring to the Cardinals’ All-Star catcher, who has started at least 128 games behind the plate for five consecutive years. “You can’t ask for more because of the demands of the position — that’s the price you pay for catching. But 130-135 [games], that’s about right.”

It’s also a level that Mauer reached only once in his 10-year career as a catcher, back in 2008; in fact, since his debut as a 20-year-old on April 5, 2004, Mauer, 30, has started only 885 games behind the plate, or just 54.6 percent of the Twins’ 1,622 regular-season games in that time. And since his contract extension went into effect in 2011, a variety of injuries limited Mauer to a mere 192 starts at catcher, or 39.5 percent of the schedule.

Knee surgery, back pain and the ill-described “bilateral leg weakness” put him on the disabled list for at least a month in five different seasons, and last August’s 90-mph blow to the head, a foul ball that jarred his catcher’s mask and triggered nearly three months of queasy symptoms, was the worst yet.

“I can’t remember any year when I’ve had so many foul tips, especially taking them off the head,” he said in May, three months before another one ended his season. “I’ve probably taken 12-15 balls off my head already this year. You don’t want to mess around with [your head], especially with concussions.”

Had hoped to catch again

Yet even when he remained sensitive to light and noise a month after the season, even when he had to leave the room to clear his head when his 6-month-old twin daughters cried, Mauer was reluctant to give up the position he has played since junior high.

“I think I kept visiting different doctors,” he said, “hoping that somebody would tell me that it was OK to get back behind there.”

Instead, the general manager told him it wasn’t. Ryan met with Twins doctors shortly after the season, and after hearing their prognosis — that Mauer, having suffered a major concussion, was at greater risk of a reoccurrence, and potentially long-term consequences — decided that the time had come for the team’s most valuable property to be moved out of harm’s way. Even if it meant that Mauer’s value, the likelihood that he would be worth the $115 million the Twins still owe him, would decline severely by moving him from the most difficult defensive position on the diamond to the easiest.

“Money isn’t a factor. It doesn’t matter if it’s Joe or anyone else — you’ve got to weigh the risk to someone’s life,” Ryan said. “It was the right thing to do.”

Ryan consulted with Shapiro and met with Mauer and his wife, Maddie, urging him to give up catching.

“The person who least wanted to accept the decision was Joe,” Shapiro said. “He just loved being a catcher. It was a major give-up for him to have to move away from that position.”

It made sense to everyone, though, including another concussion victim: former teammate Justin Morneau, who “actually told me, ‘Joe, you need to move on. It’s just not worth it,’ ” Mauer recalled.

Finally, he said, he realized “I’m a husband and father first. ... It wasn’t a tough decision, but it was, just because I love to catch and I’ve put in so much work to become the catcher that I was.”

Now he’s got a lot more work, because even Mauer admits that until now, his approach to his new position was more as a hobby than a scholarly pursuit.

“Playing first base was kind of a day off [from] catching. I kind of went out there as, ‘Do your best, and whatever happens, happens,’ ” said Mauer, who has 54 career starts at first, though only eight last year. “Now it’s my job, and I’d better do a good job.”

The Twins have tutors lined up to help him drill down on the finer points. Paul Molitor and Rod Carew, Hall of Fame hitters who ended up at first base after years elsewhere in the infield, will be in Fort Myers for daily consultation, and Molitor joins the major league coaching staff full time this year.

And former manager and first baseman Tom Kelly has long concentrated on the first basemen in spring training, helping Morneau become a solid defensive player.

“Joe has a pretty good grasp of it; we’ve had a few sessions, and now that he can devote his full attention to it, you might be able to get into a little more [detail]. I’ve got a couple of things in mind that I’d like to pass on to him,” Kelly said. “It takes a lot of repetition, but he’s such a good athlete, he’ll be fine.’’

The goal: 150 games

Mauer said he believes he will benefit from fresher legs and fewer bruises. He’s focused on regaining lost flexibility this winter, and already notices the difference in focusing less extensively on his legs during winter workouts.

“He’s got a lot of the requisites for being a good first baseman,” Ryan said. “His [6-5] size is ideal, he’s a perfect target. He’s athletic, agile, and he’s got the instincts for it. If he had stiff hands, you’d be worried.”

Mauer’s range and glove have ranked slightly above average for the position, according to spray-chart and statistical analysis by sabermetric site Baseball Prospectus.

“His athleticism and reaction times will benefit him. He does a good job moving to his right, in particular,” BP analyst Nick Wheatley-Shaller said. “If he adapts like [Boston’s] Mike Napoli did, he’s not going to hurt you out there.”

The Twins hope Mauer can play 150 games this season, as 12 major league first basemen did in 2013, as Morneau has done four times.

“I’m excited to see how I feel in August,” when he’s normally beaten up by months of foul tips, Mauer said. “Justin said, ‘You won’t believe how much better you’ll feel.’ ”

The Twins will feel the same way if Mauer continues to compile a .400 on-base percentage, as he has done six times, and whack 30 doubles, as he’s also done a half-dozen times. But major league teams received an average of 23.8 home runs from their first basemen in 2013, a level that Mauer has reached (or even approached) only once. Mauer slugged 28 homers during his MVP season in 2009, 16 of them in the Metrodome. Considering he has hit only 10 career homers at Target Field, it’s unlikely that Mauer will provide the power that most teams crave at the position.

“That’s all right. There have been some pretty good first basemen who were doubles-type hitters. You can win with them,” Ryan said. “I don’t see Joe changing his swing, changing his strike zone, just because he’s over at first. We wouldn’t want him to.”

Ryan declined to say that this is the last position change Mauer might be asked to undertake. The GM says the All-Star is “athletic enough to play a lot of positions.’’

That versatility may come into play someday if Miguel Sano, the minor leagues’ top slugging prospect, proves too big to remain at third base, as many scouts project, and winds up at first base. Ryan insists that the Twins are committed to Sano as a third baseman, for now.

“We’ve got a first baseman, and a good one,” Ryan said. “I’m excited to see what he’ll do there.”

Now the Twins must look for another catcher, five years before they had planned. But Mauer’s agent believes the Twins and Mauer will be happy with how things turn out.

“In the long run, when the team returns to its winning ways, as I know they will under Terry, and Joe delivers the hits that he will deliver, I think everyone will feel that what value was lost was de minimis compared to what was gained in this,” Shapiro said. “Sometimes things don’t work out the way you expect, but Joe is still one of the best hitters there is. That hasn’t changed.”