Although I now have a series 7, my series 0 still works well and does everything that it was meant to do. Battery life is still pretty good as well because I don’t do anything with it. If I just use it to tell the time and get texts. last week I tested it and it lasted from 2 PM to 8 AM the next day.
If you can’t remember that you even own this watch, much less what generation it is, you may not remember the password that you used to get in either. If it is password-protected, then it is worthless except for parts.