diff -Naur kdebase-workspace-4.3.98.orig/plasma/generic/applets/battery/battery.cpp kdebase-workspace-4.3.98/plasma/generic/applets/battery/battery.cpp
--- kdebase-workspace-4.3.98.orig/plasma/generic/applets/battery/battery.cpp	2010-01-31 20:30:45.000000000 +0100
+++ kdebase-workspace-4.3.98/plasma/generic/applets/battery/battery.cpp	2010-02-01 22:44:24.000000000 +0100
@@ -61,6 +61,7 @@
 #include <Plasma/CheckBox>
 #include <Plasma/ComboBox>
 #include <Plasma/IconWidget>
+#include <Plasma/ToolTipManager>
 
 
 Battery::Battery(QObject *parent, const QVariantList &args)
@@ -224,6 +225,8 @@
                                  qRound(contentsRect().height() / 10)));
         update();
     }
+    
+    Plasma::ToolTipManager::self()->registerWidget(this);
 }
 
 void Battery::dataUpdated(const QString& source, const Plasma::DataEngine::Data &data)
@@ -254,6 +257,11 @@
         setStatus(Plasma::ActiveStatus);
     }
 
+    // if the tooltip is visible, keep the displayed data up-to-date
+    if (Plasma::ToolTipManager::self()->isVisible(this)) {
+        toolTipAboutToShow();
+    }
+
     updateStatus();
     update();
 }
@@ -994,4 +1002,47 @@
     return m_acAlpha;
 }
 
+void Battery::toolTipAboutToShow()
+{
+    int battery_num = 0;
+    int battery_charge = 0;
+    bool has_battery = false;
+    QHashIterator<QString, QHash<QString, QVariant > > battery_data(m_batteries_data);
+    while (battery_data.hasNext()) {
+        battery_data.next();
+        if (battery_data.value()["Plugged in"].toBool()) {
+            battery_charge += battery_data.value()["Percent"].toInt();
+            has_battery = true;
+            ++battery_num;
+        }
+    }
+    if (battery_num > 1) {
+        battery_charge = battery_charge / battery_num;
+    }
+
+    QString  content = "";
+    QString state = battery_data.value()["State"].toString();
+    if (state == "Discharging") {
+        content += i18n("Discharging: %1% charged", battery_charge);
+    }
+    else if (state == "Charging") {
+        content += i18n("Charging: %1% charged", battery_charge);
+    }
+    else if (state == "NoCharge") {
+        content += i18n("Fully charged (%1%)", battery_charge);
+    }
+
+    if (m_showRemainingTime && (state=="Charging" || state=="Discharging" )) {
+        QTime t = QTime(m_hours, m_minutes);
+        KLocale tmpLocale(*KGlobal::locale());
+        tmpLocale.setTimeFormat("%k:%M");
+
+        content += "<br/>";
+        content += i18n("Estimated time remaining %1").arg(tmpLocale.formatTime(t, false, true)); // minutes, hours as duration
+    }
+
+    Plasma::ToolTipManager::self()->setContent(this, Plasma::ToolTipContent(content, "", KIcon("battery")));
+}
+
+
 #include "battery.moc"
diff -Naur kdebase-workspace-4.3.98.orig/plasma/generic/applets/battery/battery.h kdebase-workspace-4.3.98/plasma/generic/applets/battery/battery.h
--- kdebase-workspace-4.3.98.orig/plasma/generic/applets/battery/battery.h	2010-01-20 00:19:14.000000000 +0100
+++ kdebase-workspace-4.3.98/plasma/generic/applets/battery/battery.h	2010-02-01 22:44:24.000000000 +0100
@@ -71,7 +71,8 @@
         virtual void hoverLeaveEvent(QGraphicsSceneHoverEvent *event);
         void configAccepted();
         void readColors();
-
+        void toolTipAboutToShow();
+        
     protected:
         void createConfigurationInterface(KConfigDialog *parent);
         void setEmbedded(const bool embedded);