1. The memory that holds channel programming does not require battery power to retain its memory. The most common reason this scanner loses its programming is because power sources are switched while the scanner is on (plugging in an AC adapter while on batteries, etc).
2. To do what you want, power OFF the scanner. Turn ON the power and WHILE the "sign on message" is being displayed press PGM. The scanner should prompt you as to whether or not you want the preset channels reprogrammed.
3. Those default frequencies are only intended to get people by until they can program the correct frequencies for your area. You would be much better off programming in specific stuff you want to hear that is in your area.