Batteries almost certainly will get cheaper. Lithium isn't particularly rare. There are sources where it isn't economical to extract it currently. That's what "reserves" measure: a source that is economical to extract right now.

We tend to find new ways to extract minerals, which expands our reserves. Happens all the time, and lithium is no exception. The big one right now is the Salton Sea and seawater extraction in general.

There's also an interesting (string-based method)[https://engineering.princeton.edu/news/2023/09/07/revolutionizing-lithium-production-string] that could bring costs down and avoid the large pools of water that cause environmental damage and high water usage of current methods. It still needs to be proven at scale, however. I usually don't like to focus on any singular advancement; battery tech advances by trying 100 things, and 10 of them are practical at scale. This one does look promising, though.