To the dismay of electric-vehicle customers,Glori-Anne Gilbert Archives delivery dates for some customers who ordered Tesla's Model 3 all-electric sedan have been pushed back — again.

Refreshingly, on Tesla's Q4 earnings call Wednesday, CEO Elon Musk was contrite, and transparent about the cause of the delay.

"While there were challenges associated with Model 3 ramp, we were in a deeper level of hell than we expected," Musk said. "Still a few levels deeper than we'd like to be, but swiftly exiting, I think."

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The Model 3 is Tesla's first mass-production vehicle with an affordable price. It delivered its first Model 3's in July 2017, but since then, it's struggled with production bottlenecks and repeated delays.

On the earnings call, Musk took responsibility for the production ramp miscalculations. He explained that the challenge was in battery production, which he called "ironic," because "our battery modules really should be the thing we're best at."

"I think in part we were probably a little overconfident, a little complacent, in thinking this is something we understand," Musk said. "We put a lot of attention on other things and just got too comfortable with our ability to do battery modules, because we've been doing that since the start of the company."

It turns out that two of the production specs for two of the battery zones that were outsourced for manufacturing "flat out didn't work." Tesla had to redesign them and accelerate a production system from 18 months to 6 or 9 months. Now, Musk says he is cautiously confident that they will be able to ramp up weekly production to 2,500 cars in March, and 5,000 by the end of Q2.

"If we can send a roadster to the asteroid belt," Musk said, "We can probably solve Model 3 production. It's just a matter of time."