How can a battery operated clock with Westminster Chimes adjust itself?

My mother has this battery operated clock that does Westminster Chimes (chimes every quarter hour) and I recently put fresh batteries in it which were 2 "C" batteries (uming one for the pendulum/movement, and the other for the chimes) the clock was at 2:00 and it was about 8:30, and my mother, and I thought it would be screwed up because the time and chimes would be incorrectly. Well when it did it's first chime with the new batteries, which was 8:35 it did the full Westminster Chime, and stuck 14, and in 15 minutes, it did the quarter chime, and at 9:00 it did the full chime, and stuck 9 times. How can such a clock know what time it is, and how can it adjust it self. I never heard of a clock doing a such thing.