We're hardly the first site to raise questions about Tesla Motors and the challenges it faces. But now another piece of the puzzle has fallen into place: Daimler AG has purchased "nearly 10 percent" of the Silicon Valley electric-car startup.

That gives Tesla access to the Mercedes-Benz parts bin, which could help it get the promised 2012 Tesla Model S electric sports sedan launched.

The big question that will determine Tesla's future: What did Daimler pay for its stake? Unlike previous Tesla funding events, no dollar figures were given for the new funding. The only comment was that the stake was for "double digit millions".

That could mean anything from $10 million--which would be dire straits indeed--to $99 million, in which case the nascent car company would be valued at $1 billion.

Industry analysts say to launch a higher-volume sedan requires at least a few hundred million dollars. Tesla's finances are fairly opaque, but one former Tesla insider we contacted fears that the lack of a stated valuation means the number was on the low side. Only time will tell.

Batteries going both ways

Daimler and Tesla are hardly strangers. The two companies announced their first partnership at the 2009 Detroit Auto Show. Tesla agreed to supply batteries for 1,000 electric versions of the Smart ForTwo, to be tested in Germany and Italy.

Observers have long been skeptical that Tesla's complex liquid-cooled battery, which uses thousands of small commodity lithium-ion cells wired together in a dense network of sensors, connectors, and controllers, can be practically scaled up to produce tens of thousands of less expensive sedans a year.

Now it looks like the battery technology may flow in both directions.  Automotive News notes that CEO Elon Musk specifically cited the lithium-ion cell developed by Daimler's joint venture with Evonik, named Deutsche Accumotive GmbH, as being of interest to Tesla.

That cell is packaged in a pouch, rather than the cylindrical packaging of the commodity cells Tesla now uses, which gives additional flexibility in battery design and makes cooling much easier.

What goes up must come down

When Tesla unveiled its all-electric Roadster a couple of years ago, the company drew more media for a time than any other sports-car maker.

And there's no denying that the 2009 Tesla Roadster is hellacious fun to drive, despite questions over its range and degradation of its battery pack over the long term.

But after missed deadlines and executive turmoil, the tide seems to have turned. And inaccurate statements by CEO Elon Musk probably haven't helped. Today, skepticism runs rampant over the company's future, its funding, and its ability to launch the 2012 Tesla Model S four-door sports sedan it previewed in March.

We got a ride in that prototype last month, at a swanky Manhattan event where Tesla took deposits for the Model S and offered rides to select guests. For all of 90 seconds, it was smooth, quiet, fast, and luxurious.

Model S = CLS underneath?

But the prototype may not be quite as final as it appeared. The Daimler partnership will likely let the 2012 Tesla Model S incorporate a lot more Mercedes-Benz in it than the company told us a few weeks ago.

Tesla had offered fairly detailed specs for the new electric sedan at the preview, but executives later noted that the prototype could change considerably  in form and detail before it reached production.

Before the launch, we had asked Tesla about a story first suggested by Autoblog.nl suggesting that the running Model S prototype was built entirely on the understructure of a Mercedes-Benz CLS.

A Tesla insider told us, "the driveable prototype will be a CLS chassis with a 'mule' [e.g. jury-rigged] powertrain and a custom body and interior." Rumor had it the firm Metalcrafters was hired to "depopulate" the CLS sheetmetal from the understructure, turning it into the undeniably sleek Model S.

Tesla communications manger Rachel Konrad vehemently denied that idea, saying the prototype was entirely hand-built and had no other vehicle underneath it. We don't do "he said, she said" stories, so we dropped it.

Parts bin, or whole car?

Whether or not the Model S has CLS under the surface, it's very likely that Tesla will draw on the Mercedes-Benz parts bins for basic components of the Model S. Developing brakes, suspensions, and safety systems is surprisingly expensive, and if Tesla is to have any chance of launching the Model S for 2012, it can't possibly develop those on its own.

The bigger question is whether Tesla bases the entire car on another platform, as it did the Roadster. That car is based on a modified understructure from the lightweight two-seater Lotus Elise.

If the CLS were to be used as the base vehicle--or more likely the next generation of CLS, scheduled for 2011--potential Model S buyers had better hope it goes on a diet.

The current US-spec CLS550 has a curb weight over 4,000 pounds, and consider that one-third of the 2,400-pound 2009 Tesla Roadster's weight is the battery. The base Lotus Elise, mind you, weighs less than 2,000 pounds.

Even after removing a V8 engine and seven-speed automatic transmission, you're going to need one heavy battery to move a CLS-based Model S from 0 to 60 mph in the promised 6 seconds.

Today, Tesla continues to chew through its backlog of Roadster deliveries. The company also announced it has taken deposits on more than 1,000 Model S sedans for delivery three or four years hence.

We'll be waiting eagerly to learn more about what the Model S is actually built of. So, we suspect, will those 1,000-plus future owners.

Tesla Model S overlaid with Mercedes-Benz CLS [SOURCE: Autoblog.nl]

Tesla Model S overlaid with Mercedes-Benz CLS [SOURCE: Autoblog.nl]

[SOURCES: Automotive News (subscription required), Jalopnik]