Are you using battery thresholds and keeping your laptop connected? There is a bug in ThinkPads, at least with my t480, in which the batteries get discharged over time but doesn't get reported which causes the sudden power off. If you are using TLP I suggest you to either force a full charge or a recalibration to charge your battery properly.
Also don't discard the possibility of having a broken battery.
Are you using battery thresholds and keeping your laptop connected? There is a bug in ThinkPads, at least with my t480, in which the batteries get discharged over time but doesn't get reported which causes the sudden power off. If you are using TLP I suggest you to either force a full charge or a recalibration to charge your battery properly. Also don't discard the possibility of having a broken battery.