You might want to have a look at the power management system's logs. There may or may not be something useful in there, but it's free and easy to do - so why not?
You can run
pmset from a terminal window; it has a number of options, and they are documented in the system manuals. You can peruse the
pmset manual as follows:
$ man pmset
To get right to viewing the output, you might want to first check the battery status, then watch the raw log for a bit:
$ pmset -g batt # battery status
$ pmset -g rawlog # monitor log; use ^C to stop & return to cmd prompt
Your output may look something like this (from my system, a 2016 MacBook Pro):
$ pmset -g batt
Now drawing from 'Battery Power'
-InternalBattery-0 (id=4391011) 61%; discharging; 3:27 remaining present: true
$ pmset -g rawlog
pmset is in RAW logging mode now. Hit ctrl-c to exit.
* Battery matched at registry = 7171
No AC; Not Charging; 65%; Cap=4083: FCC=6197; Design=6669; Time=3:55; -1042mA; Cycles=285/1000; Location=0;
Polled boot=05/05/19 17:55:34; Full=05/05/19 18:15:34; User visible=05/05/19 18:19:34
No AC; Not Charging; 65%; Cap=4077: FCC=6206; Design=6669; Time=4:27; -917mA; Cycles=285/1000; Location=0;
Polled boot=05/05/19 17:55:34; Full=05/05/19 18:15:34; User visible=05/05/19 18:20:34
Perhaps the most useful item in the rawlog display is the current consumption:
An abnormal current draw may suggest a system issue; otoh, a "normal" current draw may suggest the battery itself is the issue.