Plane: make batter failsafe docs clearer

ArduPlane/Parameters.pde

@@ -414,7 +414,7 @@ const AP_Param::Info var_info[] PROGMEM = {
 
     // @Param: FS_BATT_VOLTAGE
     // @DisplayName: Failsafe battery voltage
-    // @Description: Battery voltage to trigger failsafe. Set to 0 to disable battery voltage failsafe. If the battery voltage drops below this voltage then the plane will RTL
+    // @Description: Battery voltage to trigger failsafe. Set to 0 to disable battery voltage failsafe. If the battery voltage drops below this voltage continuously for 10 seconds then the plane will switch to RTL mode
     // @Units: Volts
     // @Increment: 0.1
     // @User: Standard
@@ -422,7 +422,7 @@ const AP_Param::Info var_info[] PROGMEM = {
 
     // @Param: FS_BATT_MAH
     // @DisplayName: Failsafe battery milliAmpHours
-    // @Description: Battery capacity remaining to trigger failsafe. Set to 0 to disable battery remaining failsafe. If the battery remaining drops below this level then the plane will RTL
+    // @Description: Battery capacity remaining to trigger failsafe. Set to 0 to disable battery remaining failsafe. If the battery remaining drops below this level then the plane will switch to RTL mode immediately
     // @Units: mAh
     // @Increment: 50
     // @User: Standard