bought JVC RVNB50 Portable CD Boomblaster power Source: AC 230V, 50Hz battery DC 15V; "R20/D (13D) battery x 10 DC (car battery) 12 V now my question, as dancer wanna use the stereo outdoor for the trainings, gigs...etc, mostly now in summer what is the best and cheapest power supply i can get to play music outdoor except using those bloody expensive 10 batteries type D which won't last for long. Prox. usage of stereo outdoor between 2-6 hours