My radio was not holding date, all time when I apply power, its is reset time, and need to set clock.
After some search I found a datasheet with pinout of RS500 module, and other information, can have a optional super capacitor to maintain power to RTC. After some inspection, a found what capacitor is fault, not retain charge. I replace it with a 3V rechargeable battery, charged by 1.6V. Now I have a RTC working after power cut.