The larger model is only meant to be used on occasion, as backup power in the event of a disruption. Because of that, it isn’t meant to be continually charged and discharged — it’s only meant to last through 500 cycles. The 7 kWh model, on the other hand, is meant to last through 10 years of daily use. Tesla even says that by “modifying the way it is installed in a home,” the smaller model can be used for backup power, too.

Tesla stops selling its biggest Powerwall because people prefer the small one | The Verge