To spell out a few things: the price of lithium batteries is decreasing. Since they are the most energy-dense batteries, this is great for the cost of electric cars, and maybe for the introduction of new portable devices, but it isn't relevant to much else. In particular, performance is not improving. Moreover, there is no reason to expect them to ever be cheaper than existing less dense batteries. In particular, there is no reason to expect that the cost of storing electricity in batteries will ever be cheaper than the cost of the electricity, so they are worthless for smoothing out erratic sources of power, like wind.