I do lots of testing of apps in real phones, not emulators.
The thing is that the phones must be connected to the PC all day. Because of this, phones battery get swollen and I have to buy phones regularly.
Do you know any android phone which can be connected and on all day all week without getting swollen after a time?
Must be real phones, emulators are descarted.
I think there is a way to customise the battery charging level such that it considers 100% to be a lower charge, eg 70-80%. This should mitigate that issue somewhat, as that range of charge is what you’re supposed to store the battery at long term.
My guess is this would be done with a custom kernal for the phone. You would need a phone where you can unlock the bootloader.
Some ROMs include this by default. If you’re rooted, there’s also apps that can do this as well.