A new certificate issued by the Bluetooth Special Interest Group (or Bluetooth SIG) confirms in no uncertain terms that Samsung has a device called the Galaxy M51 in the works. Other recent leaks strongly suggest this phone will come with a battery rated for 7000mAh in capacity. It is also possible it will act as an M40 successor in 2020.
https://www.notebookcheck.net/Samsung-will-launch-the-Galaxy-M51-this-year-new-leak.481688.0.html