diff --git a/src/up-daemon.c b/src/up-daemon.c
index 38d49d5..ca780b2 100644
--- a/src/up-daemon.c
+++ b/src/up-daemon.c
@@ -169,6 +169,8 @@ up_daemon_update_display_battery (UpDaemon *daemon)
 		gdouble percentage = 0.0;
 		gdouble energy = 0.0;
 		gdouble energy_full = 0.0;
+		gdouble energy_full_design = 0.0;
+		gdouble effective_energy_full = 0.0;
 		gdouble energy_rate = 0.0;
 		gint64 time_to_empty = 0;
 		gint64 time_to_full = 0;
@@ -183,6 +185,7 @@ up_daemon_update_display_battery (UpDaemon *daemon)
 			      "percentage", &percentage,
 			      "energy", &energy,
 			      "energy-full", &energy_full,
+			      "energy-full-design", &energy_full_design,
 			      "energy-rate", &energy_rate,
 			      "time-to-empty", &time_to_empty,
 			      "time-to-full", &time_to_full,
@@ -253,11 +256,39 @@ up_daemon_update_display_battery (UpDaemon *daemon)
 		/* If at least one battery has charge thresholds enabled, propagate that. */
 		charge_threshold_enabled_total = charge_threshold_enabled_total || charge_threshold_enabled;
 
-		/* sum up composite */
+		/* Validate battery capacity data before aggregation.
+		 * Some firmware/ACPI implementations report energy_full=0 due to bugs,
+		 * which breaks the weighted percentage calculation. We fall back to
+		 * energy_full_design if available, or skip the battery from capacity-based
+		 * calculation (will use percentage averaging instead).
+		 */
+
+		if (energy_full >= 0.01) {
+			/* Primary: Use reported full capacity */
+			effective_energy_full = energy_full;
+		} else if (energy_full_design >= 0.01) {
+			/* Fallback: Use design capacity */
+			effective_energy_full = energy_full_design;
+			g_debug ("Battery reports invalid energy_full (%.4f Wh), "
+				 "using energy_full_design=%.2f Wh as fallback",
+				 energy_full, energy_full_design);
+		} else {
+			/* No valid capacity data - skip from energy-based calculation.
+			 * The percentage averaging fallback will be used instead.
+			 */
+			g_warning ("Battery reports energy=%.2f Wh but both energy_full and "
+				   "energy_full_design are invalid; excluding from composite "
+				   "capacity calculation", energy);
+			percentage_total += percentage;
+			num_batteries++;
+			continue;
+		}
+
+		/* Sum up composite using validated capacity data */
 		kind_total = UP_DEVICE_KIND_BATTERY;
 		is_present_total = TRUE;
 		energy_total += energy;
-		energy_full_total += energy_full;
+		energy_full_total += effective_energy_full;
 		energy_rate_total += energy_rate;
 		time_to_empty_total += time_to_empty;
 		time_to_full_total += time_to_full;
@@ -273,8 +304,9 @@ up_daemon_update_display_battery (UpDaemon *daemon)
 	g_debug ("Calculating percentage and time to full/to empty for %i batteries", num_batteries);
 
 	/* use percentage weighted for each battery capacity
-	 * fall back to averaging the batteries.
-	 * ASSUMPTION: If one battery has energy data, then all batteries do
+	 * Fall back to averaging the batteries if capacity data is unavailable.
+	 * NOTE: We now validate capacity data per-battery, as some firmware/ACPI
+	 * implementations incorrectly report energy_full=0.
 	 */
 	if (energy_full_total > 0.0)
 		percentage_total = 100.0 * energy_total / energy_full_total;