Index: firmware/powermgmt.c
===================================================================
--- firmware/powermgmt.c	(revision 23328)
+++ firmware/powermgmt.c	(working copy)
@@ -282,17 +282,14 @@
     else
 #endif
     /* discharging: remaining running time */
-    if ((battery_millivolts + 20) > percent_to_volt_discharge[0][0]) {
+    if (battery_millivolts > percent_to_volt_discharge[0][0]) {
+        /* linear extrapolation */
         powermgmt_est_runningtime_min = (level + battery_percent)*60
                 * battery_capacity / 200 / runcurrent();
     }
-    else if (battery_millivolts <= battery_level_shutoff[0]) {
+    if (0 > powermgmt_est_runningtime_min) {
         powermgmt_est_runningtime_min = 0;
     }
-    else {
-        powermgmt_est_runningtime_min =
-            (battery_millivolts - battery_level_shutoff[0]) / 2;
-    }
 
     battery_percent = level;
     send_battery_level_event();