Cheap 36 ~72 v to 12v 10amp output converter, haven't tried it but wil grab one with my next order.
http://www.banggood.com/Motorcycle-Electric-Cars-48V-60V-to-12V-DC-Converter-p-959438.html
http://www.banggood.com/Motorcycle-Electric-Cars-48V-60V-to-12V-DC-Converter-p-959438.html