Actually, lithium is a very depletable resource just like oil and coal are. Not in the sense that we use it up for energy, but in the sense that if you want to run all cars on lithium batteries there simply isn't enough easily mine-able lithium in the world. In this sense it is valid to say that we mine batteries. The same story goes for most solar panels.

Comparing the energy density of gasoline with the energy density of a charged battery is obviously also valid.