Have built a small solar panel system to power some garden LED lights. However, I am having trouble with charging the battery. Lights work for 1 night then off for 2-3 days. System is: 20w solar panel, 12v 30a pwm solar charge controller, 12v 18ah battery powering 6x3w LED Cree lights with 700mA flex block buck-boost DC driver. Is the solar panel too small to charge the battery in one day? Panel is in a location where it gets sun most of the day. Panel specs say it produces 1.23A but I've never been able to measure. Voltage shows 19v in full sun. Any help greatly appreciated.