if ur going to still ride ur bike on the street after u do the 24v start brock makes a box that charges both batt.. at 12 but when u hit the start button it goes 24v its nice if ur going to ride it on the street im not going to so i didnt get it for mine http://prostores2.carrierzone.com/servlet/brockracing/-strse-2744/12-dsh-24-Volt-Starter-Box/Detail