Original (not Dell) Area-51 m15x battery needed

I need a battery source and/or part number for my MIAMI-built m15x. Yes, it's still running strong but I've been using it daily without a battery because I quit using it mobile some years ago. Due to recent death of my wife, I'm going to go mobile again for quite a while. You guys have always been good to me and I sincerely appreciate your help.

Regards and a healthy, happy and prosperous 2020 to all,