I have had accubattery for my phome’s duration and Sony have the feature that you can force stop charging at 80%. In the past 3.5 years with the phone, I have charged 1 814 046 mAh in that time. Assuming avg 3.8V (not hitting too much or CV with 80%) and my local price of 0.32€/kWh, that is only 2.14€ over 3.5 years.

Phones are absolutely crazy efficient.