diff --git a/lxpanel/src/plugins/batt/batt_sys.c b/lxpanel/src/plugins/batt/batt_sys.c
index 62445fe..7b7def5 100644
--- a/lxpanel/src/plugins/batt/batt_sys.c
+++ b/lxpanel/src/plugins/batt/batt_sys.c
@@ -217,6 +217,8 @@ void battery_update(battery *b)
 	b->percentage = 0;
     else {
 	int promille = (b->energy_now * 1000) / b->energy_full;
+	if (b->energy_now == -1 || b->energy_full == -1)
+	    promille = (b->charge_now * 1000) / b->charge_full;
 	b->percentage = (promille + 5) / 10; /* round properly */
     }
     if (b->percentage > 100)