diff --git a/README.md b/README.md
index a4d576c..2fde43b 100644
--- a/README.md
+++ b/README.md
@@ -32,6 +32,10 @@ Battery Tracker gives you a single source of truth:
 - Battery percentage — set manually or synced live from Home Assistant; resets to 100% when a charge is logged
 - Retire and unretire batteries
 
+> **Tip — measuring tested capacity:** The Panasonic BQ-CC65 charger (AA/AAA) can
+> measure the actual capacity of a cell during a charge cycle. Use the reading it
+> reports as the "Tested capacity" value when logging a capacity test.
+
 ### Devices
 - Add devices with a name, battery slot count, type (Remote Control, Flashlight, Sensor, …), and notes
 - Install batteries into devices — by brand/quantity or by picking specific batteries