There are a couple of answers here that point out the immediate problem of charging time.
There are other issues you need to keep in mind:
One is how long your Tesla can operate on that charge.
If the Tesla takes days to charge and can only operate under heavy loads for half a day, you aren't going to use that device as a farm tractor. You're going to reserve those high-effort battery charges for things of more significance. Maybe build that chassis into a fire truck, where speed and power matter a great deal and you can (hopefully) afford the downtime between charges.
Two is Tesla to work vehicle adaptation.
How difficult will it be to take a chassis (and the computer controllers) designed for road use in a sedan and retool the entire thing to work with a heavier vehicle? Can the motors in a Tesla handle the extra load if you just try to slap them into the equivalent of a farm tractor or a heavy load truck chassis (dump truck, back hoe, tractor trailer truck, etc.)? Or will the load burn out the motors? I am not an engineer, but I suspect the reconfiguration of the chassis will reduce motor life drastically, at best. And of course, the heavier the work, the shorter the battery life.
Three is battery lifespan
Tesla batteries are based on laptop batteries, but better. In laptops, those batteries begin to hold less charge over time. Laptop vendors will not give more than 1 year warranty on those batteries, because they fade with use. Now, newer batteries tend to withstand this better than they used to. And Tesla's are a few steps up from laptops now. But eventually, those batteries will begin to wear out. They just won't hold a 100% charge at some point, meaning your 6-8 hour run time drifts slowly down eventually, reducing effectiveness even more. Tesla warranties their batteries for 8 years, so I suppose you can go about that long, but past that, your life is going to dramatically fall.
Four is vehicle complexity
Books and basic tools can be found to make working on a typical 1980s-era vehicle possible. But the more advanced a vehicle becomes, the more specialized the tools and skills required to maintain that vehicle. Will your survivors have those skills? How hard will it be to acquire parts and tools to work on those systems? How many different specialized skills will be required to take a Tesla and convert it to heavy workloads? Engineers? Programmers? Electricians? My father was able to adapt a 1940s truck body to fit a 1970s truck frame/engine. He had nothing but self-learning and books for both trucks to make it happen. Modern cars are not that "easy." And all of those highly trained car maintenance folk are taken away from food production, which is a critical thing.
Five is design life
I hinted at this with the batteries, but eventually, even if the batteries fail, something will break. Your car will need things that require factories that require sub-factories that require mineral refineries that require mines. Sure, at first you can scavenge for parts. But at some point you're going to hit a wall where you need parts that either can't be found, can't be extracted, or that have exceeded their "shelf life." You have a few hundred people. They aren't going to be able to get the raw materials, build the refineries and factories, to assemble those parts.
All of the above highlight a great deal of effort required to operate machinery that runs a few hours then sits there, taking up space, for a few days.
Far more efficient plan is:
- Use gasoline while it lasts, but immediately begin gathering diesel vehicles and animals.
- Use diesel vehicles (with alternative fuels as needed) for as long as they last but continue to gather animals.
- Switch to animals. Horses, mules, oxen, etc. are your future.
Gas will expire first but is the most plentiful. So use those vehicles hard and abandon them when they fail. Gather gasoline and immediately stabilize it, but accept that this is very much a temporary solution. Use those vehicles to build your initial compound and to collect diesel vehicles.
Diesel can be renewed via cooking oil, etc. with little in the way of complex works. And they are efficient for heavy work loads. Use those vehicles to complete your compound(s) and to collect more vehicles / materials. But again, know that this is temporary.
Finally, be prepared to fail back to older, easier, technology. Immediately begin collecting horses, mules, and oxen. These creatures are self-building, low maintenance relative to EV, and can be used as food at the end of their design life. Sure, they're not perfect either. But they don't require an entire infrastructure to create, fuel, and maintain over the long term.
Farming is your future. Use what's left from the good old days while you can, but be working towards the long-term, because your survivors are effectively going to be Amish -- in lifestyle, not in religion -- within 2 or 3 generations.
Sure, they can try to gather what they can and hope to not completely backslide. But rather than devote so much effort to supporting such inefficient machines as EVs, much better to be focusing on skills that can be locally supported without requiring entire infrastructures worth of industrialization. Rather than sending half a dozen people to learn mechanics, electrical engineering, and such, send a few to study up on blacksmithing, a few to study farming, and a few to study animal husbandry/veterinary medicine. Those skills will do you more good in the short and long term.