All the extra hardware required to make that work and the time and cost of installing and removing the extra battery pack means it'll probably never cost less than just hiring a longer range vehicle for the weekend. People who really need the range wouldn't bother, they'd just buy a longer range vehicle in the first place. Or one with the extra battery pre-installed and never remove it.
Not to mention that battery prices are continuing to plummet - we're quickly approaching the point where cars are just coming with as many batteries as they can easily fit. Short range EVs are likely not going to be a thing in a few more years when it doesn't cost significantly more to make a longer range EV.