Bill Gates went to see Elon Musk in 2022, hoping to convince the fellow billionaire to give away more of his money -- the way the Microsoft founder had.

The meeting went sideways, according to Walter Isaacson's new biography, "Elon Musk," which hits stores Tuesday. CNN obtained an early copy of the book, which reveals some of the rarified world of America's billionaire class, including details of the unusual relationship between Musk and Gates. Musk is the current wealthiest man in the world and Gates had topped the list before he began steadily giving it away in his philanthropic efforts.

"Hey, I'd love to come see you and talk about philanthropy and climate," Gates texted Musk in 2022, Isaacson wrote. Musk had started a $5.7 billion charitable fund at the time — mostly for tax reasons, according to Isaacson — and Gates wanted to influence Musk's approach to philanthropy

Musk told Gates to call him directly because Musk didn't use schedulers and assistants, Isaacson wrote. Gates flew to Austin, Texas, on March 9, 2022, to visit the 10-million-square-foot Tesla Gigafactory.

"Just landed," Gates texted.

"Cool," Musk replied.

Isaacson spoke to both men and other sources to detail the conversation between the two men, noting that Gates challenged whether batteries could power large semi trucks and whether solar energy would be part of solving the climate problem. Gates said Musk was too "overboard on Mars," which Gates found "bizarre thinking" about saving humanity by moving some humans to Mars if there is a nuclear war on planet earth.

As the factory tour neared an end, Gates turned the conversation toward philanthropy. Gates and his ex-wife, Melinda, had founded one of the largest private foundations in the world, the Bill and Melinda Gates Foundation, and influenced other billionaires such as Warren Buffett and Mark Zuckerberg to give most of their fortunes toward humanitarian causes during their lifetimes. The movement they started called "The Giving Pledge has gained dozens of other ultrawealthy participants.

Musk has been criticized for his lack of charitable giving over the past decade. He got into a public spat with the UN food program chief in 2021, challenging the assertion that donating $6 billion of his stock could end world hunger.

Still, Musk gave 11.5 million shares of his Tesla stake to an undisclosed charity last year, shares worth about $1.9 billion at the time they were donated. The donation would make him the second-largest charitable donor in 2022, according to a ranking of the Chronicle of Philanthropy, which was compiled before Musk's donation. The Chronicle's ranking lists Gates as No. 1 with $5.1 billion in donations, followed by Michael Bloomberg at $1.7 billion.

"Most philanthropy was "bulls---," Musk told Gates, estimating only 20 cents of each dollar made a difference that way. Gates could "do more good for climate change by investing in Tesla," Musk said, according to Isaacson.

Musk then questioned Gates on why he had placed a bet against Tesla's stock, known as a "short," in hopes the share price would drop. Musk despised people who bet against his company, seeing them as mortal enemies. At that time, Gates had lost $1.5 billion betting against the stock. Gates said he apologized and said he shorted the stock because he thought he could make money doing so.

Musk told Isaacson he felt Gates was hypocritical to fight against climate change while trying to make money on the failure of a sustainable energy car company.

When Gates sent documentation about his philanthropic work and followed up with a text to Musk, Musk asked if he was still holding a short bet against Tesla. Gates admitted he was.

Musk texted back: "Sorry... I cannot take your philanthropy on climate seriously."

Musk then famously tweeted a photo of Gates in a golf shirt with a bulging belly that made him look pregnant and mocked his appearance.

"At this point, I am convinced he is categorically insane (and an a--hole to the core)," Musk texted Isaacson after the exchange with Gates. "I did actually want to like him (sigh)."

Gates was more gracious afterward. When people criticized Musk at a dinner in Washington, DC, Gates said, "there is no one in our time who has done more to push bounds of science and innovation."