Switched off phone before removal of battery
It is necessary for phone users especially Smartphone users to always switch off their phone before removing the battery because in this case, the phone itself will know that it will be short down shortly, I this case, it will get ready so when you later put it on, it will not malfunction and again all the applications and the operating system get the chance to save whatever needs to be saved and to go through their proper shut-down process.
Note that, Removing the battery without switching the phone off will immediately crash every running applications as well as the operating system(OS). It’s just like unplugging your system while it’s running. You can do it, but it’s not advice-able, a bad idea though.
Other thing is that While switching off your device, the operating system will make sure that every thing connected to the phone’s memory and external memory is properly and carefully closed.
If you remove the battery before switching off your phone, you may corrupt the memory which may lead to unexpected behavior.
Please and Please, always switch off your phone before removing the battery. That’s my best advice to you as a phone user.