Let's put some optimistic numbers together for Panasonic:
1. Tesla builds 100k cars in 2015 (they probably won't)
2. Tesla buys 100% of batteries from Panasonic (they won't - some will come from Samsung, BYD?, etc.)
3. Panasonic gets $15,000 from each battery pack (probably a little/lot less)
4. Panasonic earns 10% margins on the batteries (probably a lot less)
So this optimistic scenario leads to 100k batteries at $15k a piece or $1.5bn in sales. 10% gross margin is $150m, so net margin is less, say $100m.
That alone is not enough to make Panasonic stock move up. And this an extremely optimistic scenario.
The other value Panasonic gets is that it owns 1%? of TSLA. But such a derivative play doesn't make any sense in mind.