Tesla Motors Inc (NASDAQ:TSLA) has been working fast and furious on developing an electric vehicle that can be sold for around $35,000. Of course the biggest barrier to success is the price of batteries, and the company recently filed a patent for metal air batteries. But it might never end up using that patent, if one industry watcher is correct.

Tesla Motors

Tesla and the push for metal air

This recent patent was spotted by analyst Trip Chowdhry at Global Equities Research (via Benzinga), and it describes a hybrid battery pack which could give Tesla’s vehicles a range of 400 miles.  The battery pack contains lithium-ion and metal-air batteries, with the metal-air batteries only coming into use on long trips when the lithium-ion batteries are spent. The reason for this probably has to do with the fact that the lifetime of metal-air batteries is shortened when they are charged all of the time.

However, the materials used in them are less expensive than the materials used in lithium-ion batteries. They actually use air to get some of what they need to generate electricity. Toyota is apparently focusing its research efforts on metal-air batteries because they are less expensive.

But Kevin Bullis of Technology Review suggests that Tesla Motors Inc (NASDAQ:TSLA) may not have any plans to use the metal-air batteries at all, even though Tesla and Toyota have a fairly close relationship.

A visit to Tesla’s labs

Bullis said he visited Tesla’s labs earlier this year and heard from the company’s chief technology officer, JB Straubel, that they think the same batteries they already use in the Model S have plenty of room for improvement. Straubel’s name is the one on the patent filing for the metal-air batteries, and it’s no secret that not all patents which are filed for end up being used by the companies which filed them.

A hybrid battery like the one described in Tesla Motors Inc (NASDAQ:TSLA)’s patent filing would make sense, but Bullis thinks that at least for now, Tesla will be using good, ol’ lithium batteries.

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