diff -r 7f3095ccfcb1 src/energy/model/basic-energy-source.cc
--- a/src/energy/model/basic-energy-source.cc	Thu May 05 12:17:12 2016 +0200
+++ b/src/energy/model/basic-energy-source.cc	Thu May 05 21:34:06 2016 -0400
@@ -40,10 +40,16 @@
     .AddConstructor<BasicEnergySource> ()
     .AddAttribute ("BasicEnergySourceInitialEnergyJ",
                    "Initial energy stored in basic energy source.",
-                   DoubleValue (10),  // in Joules
+                   DoubleValue (0),  // in Joules
                    MakeDoubleAccessor (&BasicEnergySource::SetInitialEnergy,
                                        &BasicEnergySource::GetInitialEnergy),
                    MakeDoubleChecker<double> ())
+    .AddAttribute ("BasicEnergySourceCapacityJ",
+                   "Energy capacity that can be stored in basic energy source.",
+                   DoubleValue (0),  // in Joules
+                   MakeDoubleAccessor (&BasicEnergySource::SetEnergyCapacity,
+                                       &BasicEnergySource::GetEnergyCapacity),
+                   MakeDoubleChecker<double> ())
     .AddAttribute ("BasicEnergySupplyVoltageV",
                    "Initial supply voltage for basic energy source.",
                    DoubleValue (3.0), // in Volts
@@ -77,6 +83,7 @@
 BasicEnergySource::BasicEnergySource ()
 {
   NS_LOG_FUNCTION (this);
+  m_energyCapacityJ = 0;
   m_lastUpdateTime = Seconds (0.0);
   m_depleted = false;
 }
@@ -91,8 +98,13 @@
 {
   NS_LOG_FUNCTION (this << initialEnergyJ);
   NS_ASSERT (initialEnergyJ >= 0);
+  NS_ASSERT (initialEnergyJ <= m_energyCapacityJ || m_energyCapacityJ == 0);
   m_initialEnergyJ = initialEnergyJ;
   m_remainingEnergyJ = m_initialEnergyJ;
+  if(m_energyCapacityJ == 0)
+    {
+      m_energyCapacityJ = m_initialEnergyJ;
+    }
 }
 
 void
@@ -145,7 +157,11 @@
   NS_LOG_FUNCTION (this);
   // update energy source to get the latest remaining energy.
   UpdateEnergySource ();
-  return m_remainingEnergyJ / m_initialEnergyJ;
+  if(m_energyCapacityJ == 0)
+    {
+      return 0;
+    }
+  return m_remainingEnergyJ / m_energyCapacityJ;
 }
 
 void
@@ -161,6 +177,15 @@
     }
 
   m_energyUpdateEvent.Cancel ();
+  
+  if(m_energyCapacityJ == 0)
+    {
+      m_energyCapacityJ = m_initialEnergyJ;
+    }
+  if(m_initialEnergyJ == 0)
+    {
+      m_initialEnergyJ = m_energyCapacityJ;
+    }
 
   CalculateRemainingEnergy ();
 
@@ -183,6 +208,27 @@
                                              this);
 }
 
+void
+BasicEnergySource::SetEnergyCapacity (double energyCapacityJ)
+{
+  NS_LOG_FUNCTION (this << energyCapacityJ);
+  NS_ASSERT (energyCapacityJ >= 0);
+  NS_ASSERT (energyCapacityJ >= m_initialEnergyJ || energyCapacityJ == 0);
+  m_energyCapacityJ = energyCapacityJ;
+  if(m_initialEnergyJ == 0)
+    {
+      m_initialEnergyJ = m_energyCapacityJ;
+      m_remainingEnergyJ = m_initialEnergyJ;
+    }
+}
+
+double
+BasicEnergySource::GetEnergyCapacity () const
+{
+  NS_LOG_FUNCTION (this);
+  return m_energyCapacityJ;
+}
+
 /*
  * Private functions start here.
  */
@@ -226,15 +272,18 @@
   NS_ASSERT (duration.GetSeconds () >= 0);
   // energy = current * voltage * time
   double energyToDecreaseJ = totalCurrentA * m_supplyVoltageV * duration.GetSeconds ();
-
-  if (m_remainingEnergyJ < energyToDecreaseJ) 
+  
+  // handles consuming energy below the low battery threshold
+  if (m_remainingEnergyJ <= m_energyCapacityJ * m_lowBatteryTh && energyToDecreaseJ > 0)
     {
-      m_remainingEnergyJ = 0; // energy never goes below 0
-    } 
-  else 
+      energyToDecreaseJ = 0;
+    }
+  // handles recharging above the energy capacity
+  if (m_remainingEnergyJ >= m_energyCapacityJ && energyToDecreaseJ < 0) 
     {
-      m_remainingEnergyJ -= energyToDecreaseJ;
-    }  
+      energyToDecreaseJ = 0;
+    }
+  m_remainingEnergyJ -= energyToDecreaseJ;
 
   NS_LOG_DEBUG ("BasicEnergySource:Remaining energy = " << m_remainingEnergyJ);
 }
diff -r 7f3095ccfcb1 src/energy/model/basic-energy-source.h
--- a/src/energy/model/basic-energy-source.h	Thu May 05 12:17:12 2016 +0200
+++ b/src/energy/model/basic-energy-source.h	Thu May 05 21:34:06 2016 -0400
@@ -47,6 +47,13 @@
    * Implements GetInitialEnergy.
    */
   virtual double GetInitialEnergy (void) const;
+  
+  /**
+   * \return The source energy capacity, in Joules.
+   *
+   * Implements GetEnergyCapacity.
+   */
+  virtual double GetEnergyCapacity (void) const;
 
   /**
    * \returns Supply voltage at the energy source.
@@ -80,8 +87,19 @@
    * Sets initial energy stored in the energy source. Note that initial energy
    * is assumed to be set before simulation starts and is set only once per
    * simulation.
+   * Note that if the initial energy is not set, it is assumed to be equal to 
+   * the source energy capacity.
    */
   void SetInitialEnergy (double initialEnergyJ);
+  
+  /**
+   * \param The source energy capacity, in Joules.
+   *
+   * Sets the energy capacity of the source.
+   * Note that if the energy capacity is not set, it is assumed to be equal to
+   * the initial energy.
+   */
+  void SetEnergyCapacity (double energyCapacityJ);
 
   /**
    * \param supplyVoltageV Supply voltage at the energy source, in Volts.
@@ -137,6 +155,7 @@
 
 private:
   double m_initialEnergyJ;                // initial energy, in Joules
+  double m_energyCapacityJ;               // energy capacity, in Joules
   double m_supplyVoltageV;                // supply voltage, in Volts
   double m_lowBatteryTh;                  // low battery threshold, as a fraction of the initial energy
   double m_highBatteryTh;                 // high battery threshold, as a fraction of the initial energy
diff -r 7f3095ccfcb1 src/energy/model/energy-source.h
--- a/src/energy/model/energy-source.h	Thu May 05 12:17:12 2016 +0200
+++ b/src/energy/model/energy-source.h	Thu May 05 21:34:06 2016 -0400
@@ -100,6 +100,14 @@
    * with a fixed initial energy (energy capacity), set method is not needed.
    */
   virtual double GetInitialEnergy (void) const = 0;
+  
+  /**
+   * \returns Energy capacity of the energy source.
+   *
+   * Set method is to be defined in child class only if necessary. For sources
+   * with a fixed energy capacity, set method is not needed.
+   */
+  virtual double GetEnergyCapacity (void) const = 0;
 
   /**
    * \returns Remaining energy at the energy source.
diff -r 7f3095ccfcb1 src/energy/model/li-ion-energy-source.cc
--- a/src/energy/model/li-ion-energy-source.cc	Thu May 05 12:17:12 2016 +0200
+++ b/src/energy/model/li-ion-energy-source.cc	Thu May 05 21:34:06 2016 -0400
@@ -41,11 +41,17 @@
     .SetGroupName ("Energy")
     .AddConstructor<LiIonEnergySource> ()
     .AddAttribute ("LiIonEnergySourceInitialEnergyJ",
-                   "Initial energy stored in basic energy source.",
-                   DoubleValue (31752.0),  // in Joules
+                   "Initial energy stored in LiIon energy source.",
+                   DoubleValue (0),  // in Joules
                    MakeDoubleAccessor (&LiIonEnergySource::SetInitialEnergy,
                                        &LiIonEnergySource::GetInitialEnergy),
                    MakeDoubleChecker<double> ())
+    .AddAttribute ("LiIonEnergySourceCapacityJ",
+                   "Energy capacity that can be stored in LiIon energy source.",
+                   DoubleValue (0),  // in Joules
+                   MakeDoubleAccessor (&LiIonEnergySource::SetEnergyCapacity,
+                                       &LiIonEnergySource::GetEnergyCapacity),
+                   MakeDoubleChecker<double> ())
     .AddAttribute ("LiIonEnergyLowBatteryThreshold",
                    "Low battery threshold for LiIon energy source.",
                    DoubleValue (0.10), // as a fraction of the initial energy
@@ -112,7 +118,8 @@
 }
 
 LiIonEnergySource::LiIonEnergySource ()
-  : m_drainedCapacity (0.0),
+  : m_energyCapacityJ (0.0),
+    m_drainedCapacity (0.0),
     m_lastUpdateTime (Seconds (0.0))
 {
   NS_LOG_FUNCTION (this);
@@ -128,9 +135,14 @@
 {
   NS_LOG_FUNCTION (this << initialEnergyJ);
   NS_ASSERT (initialEnergyJ >= 0);
+  NS_ASSERT (initialEnergyJ <= m_energyCapacityJ || m_energyCapacityJ == 0);
   m_initialEnergyJ = initialEnergyJ;
   // set remaining energy to be initial energy
   m_remainingEnergyJ = m_initialEnergyJ;
+  if(m_energyCapacityJ == 0)
+    {
+      m_energyCapacityJ = m_initialEnergyJ;
+    }
 }
 
 double
@@ -184,6 +196,10 @@
   NS_LOG_FUNCTION (this);
   // update energy source to get the latest remaining energy.
   UpdateEnergySource ();
+  if(m_energyCapacityJ == 0)
+    {
+      return 0;
+    }
   return m_remainingEnergyJ / m_initialEnergyJ;
 }
 
@@ -223,6 +239,15 @@
     }
 
   m_energyUpdateEvent.Cancel ();
+  
+  if(m_energyCapacityJ == 0)
+    {
+      m_energyCapacityJ = m_initialEnergyJ;
+    }
+  if(m_initialEnergyJ == 0)
+    {
+      m_initialEnergyJ = m_energyCapacityJ;
+    }
 
   CalculateRemainingEnergy ();
 
@@ -239,6 +264,27 @@
                                              this);
 }
 
+void
+LiIonEnergySource::SetEnergyCapacity (double energyCapacityJ)
+{
+  NS_LOG_FUNCTION (this << energyCapacityJ);
+  NS_ASSERT (energyCapacityJ >= 0);
+  NS_ASSERT (energyCapacityJ >= m_initialEnergyJ || energyCapacityJ == 0);
+  m_energyCapacityJ = energyCapacityJ;
+  if(m_initialEnergyJ == 0)
+    {
+      m_initialEnergyJ = m_energyCapacityJ;
+      m_remainingEnergyJ = m_initialEnergyJ;
+    }
+}
+
+double
+LiIonEnergySource::GetEnergyCapacity () const
+{
+  NS_LOG_FUNCTION (this);
+  return m_energyCapacityJ;
+}
+
 /*
  * Private functions start here.
  */
@@ -277,14 +323,17 @@
   // energy = current * voltage * time
   double energyToDecreaseJ = totalCurrentA * m_supplyVoltageV * duration.GetSeconds ();
 
-  if (m_remainingEnergyJ < energyToDecreaseJ) 
+  // handles consuming energy below the low battery threshold
+  if (m_remainingEnergyJ <= m_energyCapacityJ * m_lowBatteryTh && energyToDecreaseJ > 0)
     {
-      m_remainingEnergyJ = 0; // energy never goes below 0
-    } 
-  else 
+      energyToDecreaseJ = 0;
+    }
+  // handles recharging above the energy capacity
+  if (m_remainingEnergyJ >= m_energyCapacityJ && energyToDecreaseJ < 0) 
     {
-      m_remainingEnergyJ -= energyToDecreaseJ;
-    }  
+      energyToDecreaseJ = 0;
+    }
+  m_remainingEnergyJ -= energyToDecreaseJ;
 
   m_drainedCapacity += (totalCurrentA * duration.GetSeconds () / 3600);
   // update the supply voltage
diff -r 7f3095ccfcb1 src/energy/model/li-ion-energy-source.h
--- a/src/energy/model/li-ion-energy-source.h	Thu May 05 12:17:12 2016 +0200
+++ b/src/energy/model/li-ion-energy-source.h	Thu May 05 21:34:06 2016 -0400
@@ -90,6 +90,22 @@
    * before simulation starts and is set only once per simulation.
    */
   void SetInitialEnergy (double initialEnergyJ);
+  
+  /**
+   * \return The source energy capacity, in Joules.
+   *
+   * Implements GetEnergyCapacity.
+   */
+  virtual double GetEnergyCapacity (void) const;
+  
+  /**
+   * \param The source energy capacity, in Joules.
+   *
+   * Sets the energy capacity of the source.
+   * Note that if the energy capacity is not set, it is assumed to be equal to
+   * the initial energy.
+   */
+  void SetEnergyCapacity (double energyCapacityJ);
 
   /**
    * \returns Supply voltage at the energy source.
@@ -182,6 +198,7 @@
 
 private:
   double m_initialEnergyJ;                // initial energy, in Joules
+  double m_energyCapacityJ;               // energy capacity, in Joules
   TracedValue<double> m_remainingEnergyJ; // remaining energy, in Joules
   double m_drainedCapacity;               // capacity drained from the cell, in Ah
   double m_supplyVoltageV;                // actual voltage of the cell
diff -r 7f3095ccfcb1 src/energy/model/rv-battery-model.cc
--- a/src/energy/model/rv-battery-model.cc	Thu May 05 12:17:12 2016 +0200
+++ b/src/energy/model/rv-battery-model.cc	Thu May 05 21:34:06 2016 -0400
@@ -115,6 +115,13 @@
 }
 
 double
+RvBatteryModel::GetEnergyCapacity (void) const
+{
+  NS_LOG_FUNCTION (this);
+  return m_alpha * GetSupplyVoltage ();
+}
+
+double
 RvBatteryModel::GetSupplyVoltage (void) const
 {
   NS_LOG_FUNCTION (this);
diff -r 7f3095ccfcb1 src/energy/model/rv-battery-model.h
--- a/src/energy/model/rv-battery-model.h	Thu May 05 12:17:12 2016 +0200
+++ b/src/energy/model/rv-battery-model.h	Thu May 05 21:34:06 2016 -0400
@@ -60,6 +60,13 @@
    * Implements GetInitialEnergy.
    */
   virtual double GetInitialEnergy (void) const;
+  
+  /**
+   * \return The source energy capacity, in Joules.
+   *
+   * Implements GetEnergyCapacity.
+   */
+  virtual double GetEnergyCapacity (void) const;
 
   /**
    * \returns Supply voltage at the energy source.