We are confident that you can draw up to 15A (180W) without incident, if you use direct battery connection.  Of course, your charging system may have a much lower limit, and dirty or corroded connections could overheat at this current.

Under the usual conditions of weathering and neglect, extended currents above 7.5A may cause trouble in open air.  In an insulated space, these connections can get hot enough to burn skin with extended currents over 3.75A.