I am looking to purchase a used Tesla from private party that has free super charging. There is a super charging station right next to my office. My thought is I can super charge daily or as needed while at work.
Is daily super charging bad for the car, even if charged to say 70-80%?
Supercharging may be free but if more than 50% of the charging spaces are in use Tesla may charge you an idling fee ($1.00 per minute) if not actively charging and plugged into a Supercharger (SC).
Supercharging is quickest, most efficient when the Tesla vehicle has been preconditioned for Supercharging. If the SC is next to your workplace there won't be enough time for the Tesla vehicle to precondition before using the Supercharger. (Preconditioning for Supercharging only functions while the Tesla vehicle is being driven.) The actual Supercharger charging rate could be 1/2 or 1/3rd of the maximum charging rate depending on the battery state of charge and temperature. Tesla owners who value their time usually will precondition for Supercharging to minimize the time spent at the SC.
Tesla recommends leaving the Tesla vehicle plugged in when not in use but this applies to when plugged in at home or work, not when using a Supercharger. Depending on how far your commute and other daily driving distance is you may only need to use the SC every second or third day and on the weekend for longer trips.
Regular or exclusively charging using a SC does stress the battery more than charging at the lower kW rate when using 240V charging. The Tesla vehicle monitors and manages the SC charging session to preserve the health of the battery. The highest Level 2 (240V) kW charging rate is 11.5kW. The lowest SC kW charging rate is 72kW (6.25X higher, correspondingly faster.)
Currently there are several different generations of SC in use in the US.
Gen2 can charge at up to a maximum of either 120kW or 150kW maximum charge rate
Gen3 can charge at up to 250kW (only for about 5 minutes, then the rate starts to taper down)
Urban SC are found in parking garages, can charge at up to 72kW. The Urban SC are the slowest but may be the least stressful due to the lower maximum kW of the Urban SC.
If I could only use a SC I would seek out an Urban SC as the maximum 72kW charge rate is well within 1C where C is the capacity of the battery in kWh. Keeping the charge rate to 1C or less would be better for the long term health of the battery.