I have had my trailer for 22 years now and just added winch a few years ago , ( my wife got tired of helping me push the car in and out when it broke so she bought it for me ) my trailer was in the shop for brakes and bearings recently and I had them hook the trailer plug to the winch battery so it " charges " while I am towing . The repair shop manager told me that wiring it that way only maintains the battery like a battery tender it won't charge it from dead even if you drive a lot of miles. So imo you will still need a battery for the winch since wiring the trailer plug to the winch won't have enough power. BTW: going for the top cabinets was a good idea , I have them and they really come in handy you will be surprised how much they hold .