battery-charge alerts using a rolling mean of the last 10 valid measurements.

README.md

@@ -826,8 +826,8 @@ full-size PNG when a graph is clicked.
 The collector also sends an ntfy notification when:
 
 - The UPS status changes
-- Battery charge crosses below 50%
-- Battery charge crosses below 5%
+- Mean battery charge over the last 10 measurements crosses below 50%
+- Mean battery charge over the last 10 measurements crosses below 5%
 - Estimated battery runtime crosses below 5 minutes
 - Local Raspberry Pi shutdown is requested below 200 seconds of runtime
 
@@ -835,6 +835,9 @@ Alert state is stored in `/var/lib/rrd/bx950mi-alert-state.json`, allowing
 changes to be detected across cron runs. The first run establishes a baseline
 without sending notifications. Threshold notifications can fire again after a
 value recovers above the threshold and later drops below it.
+Battery-charge alerts start after 10 valid measurements have been collected;
+using their rolling mean prevents a single erroneous `0%` report from causing
+a false alarm. Raw measurements are still stored in the RRD and graphed.
 
 ### Automatic shutdown of the Plex server