Car batteries are not really comparable to cellphone batteries. Even among "lithium" batteries in cars there are multiple chemistries with different longevity and trade-offs (e.g. LFP can be kept charged at 100%, while NMC would rather not).
1. Cars have advanced battery management system with heating and cooling, which noticeably improves the battery life (e.g old Teslas have lost 1%-2% capacity per year over a decade, while Leaf about 3% per year, most likely due to lacking liquid cooling).
2. Cars won't let the battery discharge to 0%. Modern EVs even have an inaccessible reserve, so that when the car shows 0%, it's actually ~5%. Cars with vehicle-to-load/vehicle-to-grid typically stop giving power at 20% state of charge. Slowly cycling around 50% is quite gentle for the battery.
3. The grid just has to pay more for the storage than the cost of battery wear. The "duck curve" means they'll want to pay you to take electricity off of them at noon, and pay you a premium to get it back in the evening peak time.
1. Cars have advanced battery management system with heating and cooling, which noticeably improves the battery life (e.g old Teslas have lost 1%-2% capacity per year over a decade, while Leaf about 3% per year, most likely due to lacking liquid cooling).
2. Cars won't let the battery discharge to 0%. Modern EVs even have an inaccessible reserve, so that when the car shows 0%, it's actually ~5%. Cars with vehicle-to-load/vehicle-to-grid typically stop giving power at 20% state of charge. Slowly cycling around 50% is quite gentle for the battery.
3. The grid just has to pay more for the storage than the cost of battery wear. The "duck curve" means they'll want to pay you to take electricity off of them at noon, and pay you a premium to get it back in the evening peak time.