diff --git a/src/com/android/settings/BatteryInfo.java b/src/com/android/settings/BatteryInfo.java
index ccad23637ee..3f8827755ad 100644
--- a/src/com/android/settings/BatteryInfo.java
+++ b/src/com/android/settings/BatteryInfo.java
@@ -63,11 +63,12 @@ public class BatteryInfo extends Activity {
 
     /**
      * Format a number of tenths-units as a decimal string without using a
-     * conversion to float.  E.g. 347 -> "34.7"
+     * conversion to float.  E.g. 347 -> "34.7", -99 -> "-9.9"
      */
     private final String tenthsToFixedString(int x) {
         int tens = x / 10;
-        return Integer.toString(tens) + "." + (x - 10 * tens);
+        // use Math.abs to avoid "-9.-9" about -99
+        return Integer.toString(tens) + "." + Math.abs(x - 10 * tens);
     }
 
    /**