Quartz watches are easy to maintain because they are inexpensive and their typical accuracy is 15 seconds per month which means they may lose or gain time by 15 seconds per month on average. They are powered by a battery usually a lithium-ion cell which is usually long-life which lasts up to 3 years. So no problem there. Mechanical watches tend to be more expensive as compared to quartz. Mechanical watches are not as accurate but most modern watches are very accurate, some of them are renowned certified chronometers which are accurate to 5 seconds per day. Power comes from a mainspring which is either self-wound by the movement of the wrist which turns a rotor inside which in turn winds the mainspring. There are watches that are hand-wound only by the rotation of the crown or both, hand-wound and automatic.