PALO ALTO, Calif. (AP) — Electric car maker Tesla Motors says California is back in the running for a massive battery plant it plans to start building this year.

But Tesla CEO Elon Musk says the state is in the "improbable" category for the $5 billion lithium-ion battery factory. That's not because of economic incentives in California but because of the time it takes to get regulatory approval there.

Musk said on an earnings call Wednesday that Gov. Jerry Brown and his staff are working hard to woo the company. But Musk says groundbreaking on the first of two sites the company plans will probably come at the end of next month.

Tesla previously said just four states were in the running for the plant: Arizona, New Mexico, Nevada and Texas.