Tesla's manufacturing struggles to build the Model 3 at its Fremont, California, factory have been well documented.

The same can't be said for its partner Panasonic, as it struggles to build enough new lithium-ion batteries to power them.

A report by Business Insider, quoting three current and former employees, says that the company scraps enough material to make half a million batteries per day, out of the 3 million cells it sends to Tesla daily.

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On its face, that level of waste might be appalling. But to insiders who understand battery production, it's a sign of even bigger problems, according to the report. One of the main reasons for the waste is that material to produce the cells, from lithium-hydroxide solution to machine rollers, gets contaminated too frequently.

Like other battery manufacturing operations, Panasonic's facility at Tesla's Gigafactory in Sparks, Nevada, operates a cleanroom environment, where employees are required to wear special "bunny suits" to prevent hair, lint, body oils, or other substances from contaminating the battery materials.

The current and former employees told Business Insider of examples of scissors, tools, and a roll of tape falling into vats of chemicals being mixed into battery electrodes. "Why do we throw away half a million batteries a day? Because people are slobs and the stuff's not clean," said one former employee.

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In another case, a machine began leaking oil and the lubricant got into nearly finished batteries, leaving employees to sift through batteries for two weeks looking for those that were contaminated.

Unlike at least most other battery manufacturing operations, employees report intense pressure to work quickly to meet production goals. Last month, Tesla CEO Elon Musk on Twitter called Panasonic battery production a constraint on Tesla's Model 3 output.

Battery experts say that a piece of metal a millimeter or a half millimeter long and thinner than a human hair could cause a short in the battery or even lead to a fire.

Panasonic responded to Business Insider with a statement, saying: "Panasonic produces the most advanced electric vehicle battery cells because we pay exceptional attention to quality. Our quality-control protocols are industry standards and include clean-room environments and laboratory-like working conditions. The battery cells go through several testing gates before they are released to Tesla, and Tesla separately tests the cells after delivery."

This piece has been edited to remove mention of a battery fire and an inappropriately suggested association between it and the Gigafactory.