What can be with the battery? My MacBook Pro (13-inch, mid 2010, El Capitan) periodically turns off. And this is happening completely randomly - sometimes it works fine for more than a day, and sometimes turns itself off 10 times in an hour, sometimes just turns off when you turn on the laptop. TG Pro App after each shutdown displays the message "Forced - Battery current outside limit". The number of charge cycles: 859. Maybe I should change the battery?

UPD I changed the battery but the problem remained.
Yes you have to change your battery.

The Apple technician will confirm you it is beyond dead, as a dead spring (a battery is just a chemical spring with a finite life).