There are way way too expensive right now, and they take an hour to fully charge and the range is short.
The only way to improve those things is to make the batteries more expensive and more unstable and dangerous. There has been much improvement over the years, but Li+ battery technology isn't the same as computer chips. The physics don't provide a path to cost parity right now. There will have to be a an unforeseen breakthrough for that to occur. Could it happen in 20 years? Sure. I wouldn't bet on it.