diff --git a/src/WatchFace.cpp b/src/WatchFace.cpp
index ed31646..5e8678f 100644
--- a/src/WatchFace.cpp
+++ b/src/WatchFace.cpp
@@ -128,7 +128,7 @@ void WatchFace::DrawBatteryIcon()
   } else if (level < 0.0f) {
     level = 0.0f;
   }
-  level = 0.5f - sin(asin(1.0f - 2.0f * level) / 3.0f);
+  level = level * level * (3.0f - 2.0f * level);
 
   m_display.fillRect(200 - 44, 9, (int)std::round(35.0f * level), 15, GxEPD_BLACK);