I'm don't know a lot about electricity. I want to buy a solar collector unit to charge up a 12 volt deep cycle battery when I'm off the grid. In good sunlight how long would it take to charge -say an 80 amp.hour battery if the Solar unit has say 20 watts on capacity? I was thinking Watts = Amps x Volts so Amps = watts/volts Amps = 20 watts/12 volts = 1.67 amps Is that 1.67 amp/hours going into the battery? Would it take 80 amp/hours divided by 1.67 watt/hr to take about 48 hours of good Sun to charge the battery if it were drawn down completely? Please let me know the error of my thinking. It shouldn't take long to find some!