Base Model 3: 57.5 kWh battery.

In California, charging at 40c/kWh during the day and discharging at 85c/kWh (for evening peak) would yield about $23 daily - or $8,400 annually.

Most Tesla's retain above 90% battery capacity after 100,000 miles [1]

Completely charging and discharging daily for one year is equivalent to 99,280 miles. A new Model 3 battery pack costs $15,800 [1] currently. 10% degradation is equivalent to $1,580.

Doing this currently would provide a ~7-year payback period on a Model 3.

[1] https://evannex.com/blogs/news/tesla-model-3-battery-degrada...

[2] https://www.slashgear.com/857917/replacing-the-battery-pack-...