i=p/v
Current=power/voltage=20w/48v=0.416A
Battery cars generally use 48V 12Ah lead-acid batteries, or one tenth of the norm. capacity Charging current, if you use 1.2A current to charge for 10 hours, it can be fully charged: 12ah divided by 1.2a = 10 hours; if you use 1.8A high current charging (ordinary charger), it will take 6.6 hours for full charge, 12ah divided by 1.8 = 6.6 hours if you use solar panel, it takes 28, 8 hours to fully charge: 12 divided by 0.416 = 28.8 hours. Simply plug in the charging plug when you have nothing to do. Calculating the time spent on cloudy days, this amount of charging equates to one charge every five days with a regular charger: 28.8 divided by the charging time of 8 hours per day = 3.6 days. The loss is 1.4 cloudy days, which is roughly equivalent. to a full charge in 5 days. AVoltage regulator is required, otherwise battery life will be affected.