The best solution is a 24/12 power inverter of about the 18 amp size. Then you will have enough to run a radio CB recharge a cell phone or whatever else comes along. If you try and tap off of the battery it will cause that battery to die a slow agonizing death. It will also drive the charging system crazy, one battery will end up overcharged or one will be under charged. I work on 24/12 "stuff" daily, road graders and construction equipment for cities and counties who want to put their private band radios into their construction equipment. Let me know if I can help....Thanks Randy
