These are range extenders, and were used with the Fisker Karma, BMW i3 (as an option) and, most recently, the Mazda CX-30 with a Wankel engine. The latter was

These are range extenders, and were used with the Fisker Karma, BMW i3 (as an option) and, most recently, the Mazda CX-30 with a Wankel engine. The latter was sold in the UK/EU and was on the market for two years only.