Gundlach said that Tesla was not about the cars, a view he shared with Bloomberg's Barry Ritholtz back in July.
"Tesla is all about the batteries," he said Monday. "I think they could almost change society if they pursue battery technology that can get houses off the grid."
Tesla CEO Elon Musk is also chairman of the solar energy company Solar City.
Gundlach said this potential is particularly strong in the "sun states" like Arizona and Nevada. In September, Tesla struck a deal to build its $5 billion gigafactory in Nevada, where the company plans to build lithium-ion batteries for its electric cars.
And while Tesla will be its own battery supplier once the gigafactory goes online, the real benefit that Gundlach thinks the company could reap from this operation is the ability to sell the batteries to other companies.
Back in July, Gundlach said: "If I was Elon Musk, I might go to all the other auto companies and say, 'I'll make you a deal: I'll get out of the car business, but let's set up a long-term deal on you buying my batteries.'"
On Monday, Gundlach said Tesla had the ability to be a "major leader" but again reiterated that his bullish view on the company was about the batteries and the company's technologies, not its cars.