How can a 12V 80Ah Battery be 1800W? Shouldn't it be 960W?
80Ah means "80 ampere*hours" -- approximately, the battery can give 80 amperes * 1 hour, or 160 amperes * 0.5 hours, or 40 amperes * 2 hours. 

1800W refers to maximum power -- if you draw more than that, the battery may overheat and fail. At 12 volt, this means 150 amperes. This means that you should not discharge battery faster than that. Incidentally, this means the battery can be safely discharged in about 40 minutes.