Finding a solution to make a decent batterypack, that I can install and charge/discharge without having to remove it
First, the board you have is called &quot;Protection PCB Board&quot;. It is a very important board that makes sure that your batteries will not catch fire or become damaged from overdischarge. However, it cannot charge the batteries by itself. You need a separate charger board for that (or a special AC/DC adapter which is designed for 4S li-ion battery charging)
Second, you don't need any switches or multiple outputs -- as long as you are not drawing too much power, you can connect charger and discharger to the battery at the same time. Here is an example for 1S configuration:

Note that picture is for 1S, and you have 4S -- so you need different parts. Your &quot;li-ion battery charger&quot; board must be able to charge 4 cells, and your DC/DC converter must be power enough for your speaker.