I though about doing that but i converted my trailer to the smaller plug so it would work on just about anybodys trailer and now i have a big round plug to the small plug adapter. I was kind of strapped for time but your way would deffently be the proper way to do it . Either way as long as the batterys have a charge to start off with the altenator keeps them topped of with out any strain on it (works great ). I had 2 diesel truck batterys in there untill theives started stealing batterys and stole them . I didnt charge them but about every six months . The main reason i did this is im tired of everybody burning up my relasy in my winch trying to pull a car up with dead batterys . I love my car trailer but i hate lending it out something always happpens and it was always like that to start off with.