The partnership should help produce cheaper electric cars. When you have one of the major electronic brands teaming up with you, they should have some technology that would be cheaper or ideas to help make them more affordable. I think this is the first major step in making cheaper electric cars and getting us away from our dependency on oil.
If production rates are higher on automotive grade electric batteries then prices will be lower - as the opposite is true. If there aren't enough batteries for electric powered cars then the cost is higher. Right now, electric cars are available at a slightly higher rate than cars with fuel engines, but I myself am looking into electric vehicles because the cost of fuel alone makes it a better choice.
Tesla has been in car production for sometimes now, and given the step they have mad, that is joining hands with panasonic, soon they will be able to start the production of cost effective cars. this will be so due the might of panasonic when it comes to production of electronics devices.
Unfortunately, EVs are hampered by the fact that consumers don't seem to want them. The Volt is a great example of this. Relatively affordable, but it still suffers from poor customer demand. Until customers actually want EVs in sufficient quantity to affect prices, Tesla's partnership only makes building EVs easier not cost-effective.