According to the technical specifications for the 94Ah i3 (See: https://www.press.bmwgroup.com/global/article/search/tag:136/category:11/attach-lang:2/) it can regenerate at a rate up to 50 kW! Instead of putting in a dinky 7.68 kW (240V 32A) "Level 2" charger you could put your car on a roller...