For instance, would you carry an iPhone the size of a shoebox if the rest of the space was a battery? Would you even be willing to carry one of the 80s phones that had a satchel?
I think you need only look back at the first mobile phones in the 1980s to find your answer to that.
The first mobile phones and I mean prior to the first Nokias were undesirable at any price level due to consisting of overly heavy nicad batteries. As another mentioned: 1987 Lethal Weapon showed this issue. The only other niche market they could squeeze these stupid huge shoesized battery phones was in cars.