First you should reinstall the driver, but since it is not in the device manager, you should check what Aida64 says about the battery. If there is no battery information too, download the snappy driver installer or any similar programm (don’t update any other drivers, it can “brick” system). If the program detects the battery - try to install the driver, if not - check if the battery itself is connected.
It depends on the civil code and consumer protection of your country, for example, in my country I can open the device and disconnect any FFC without losing the warranty (but if the warranty seal is on FFC - the service center will inspect the board for a long time)
I don’t have any information about that. Maybe the laptop has an original charger detection system. Also charger and power bank must be approved to switch the voltage from 5V to 12V and I don’t think that this is implemented in a laptop.
I found that this laptop supports “PD2.0 fast charging with any PD adapter
or power bank” , so make sure you are using PD2.0 charger.