Thank u I understoodWell, if you ever pulled an old laptop off a shelf, are the batteries still charged like when you put it away?
Rechargeable Lithium batteries generally have a self-discharge rate that is not good for long term power storage.
Here is why a transistor is usedThis circuit uses transistor half-biased, it works but the transistor limits the current and gets hot, nullifying the use of old Li-ion battery, which is another topic how to isolate good cells from bad ones, it's just easier to use good Ni-MH that are usually the same capacity and lasts as long if not even longer._
The transistor is an emitter-follower with a 0.65V base-emitter voltage drop and is biased with two identical-value resistors to reduce the 4.2V battery voltage to 2.1V for the base. Then the clock gets 2.1V - 0.65V= 1.45V like a 1.5V ordinary disposable battery. The clock motor is tiny and uses a tiny current.Yes, but clock will be slowed down. Probably wont work properly.
He only limit current....