1 You need to disassemble your perpetual calendar first. Obtain power supply parameters. Such as voltage and current. In particular, the size of the current is important. If the current is very large, the battery needs to be changed often after the change, which is very troublesome.
2 For single power supply. Select multiple batteries to supply power in series according to the supply voltage.
3 Since most perpetual calendars are ultra-thin, there is no room for battery boxes. This is when the transformation is difficult.
4 If you know the circuit. The booster circuit and charge management circuit can be designed from a rechargeable battery (such as a mobile phone battery), and it is better to supply AC and DC