Your best bet is to take batteries to a disposal/reclamation facility and that should be your first option; however, that is not always possible and the last thing you should do is just throw it away.
The salt water trick isn't the answer either because that can merely corrode the positive/negative leads and leave voltage in the cell. This video shows how to completely drain a lipo. When you've completed the process shown in this video you can throw the remains in the trash.
27 апр 2020