I tried to work with LinearBatteryPlugin, LinearBatteryConsumerPlugin and FollowerPlugin, but none of them work with my URDF. For instance, every time i roslaunch my urdf file i get the following, and gazebo dies.

gzserver: /var/lib/jenkins/workspace/gazebo8-debbuilder/build/gazebo-8.1.1/plugins/LinearBatteryPlugin.cc:60: virtual void gazebo::LinearBatteryPlugin::Load(gazebo::physics::ModelPtr, sdf::ElementPtr): Assertion `(link)&&("Link was NULL")' failed. Aborted (core dumped)

The current part of the URDF (which has sdf tags but i don't know how i can modify them) is:

  <joint name="battery_joint" type="fixed">
<axis xyz="0 0 0"/>
<origin xyz="2.3 0 1" rpy="0 0 0" />
<parent link="link_name"/>
<child link="body" />
  </joint>


<link name="body">
  <inertial>
      <mass value="10" />
      <origin xyz="0 0 0" />
      <inertia ixx="1.8" ixy="0.0" ixz="0.0" iyy="1.8" iyz="0.0" izz="1.8"/>
  </inertial>
   <visual>
    <origin xyz="0 0 0" rpy="0 0 0" />
    <geometry>
        <box size = "1 1 1"/> 
    </geometry>
   </visual>
    <collision>         
    <geometry>
        <box size = "1 1 1"/> 
    </geometry>
      <surface>
        <friction>
          <ode>
            <mu>0.1</mu>
            <mu2>0.1</mu2>
          </ode>
        </friction>
      </surface>
    </collision>
    <battery name="linear_battery">
      <voltage>12.592</voltage>
    </battery>
</link>
  <gazebo>
      <plugin name="battery" filename="libLinearBatteryPlugin.so">
        <link_name>body</link_name>
        <battery_name>linear_battery</battery_name>
        <open_circuit_voltage_constant_coef>25</open_circuit_voltage_constant_coef>
        <open_circuit_voltage_linear_coef>-3.1424</open_circuit_voltage_linear_coef>
        <initial_charge>1.1665</initial_charge>
        <capacity>1.2009</capacity>
        <resistance>0.061523</resistance>
        <smooth_current_tau>1.9499</smooth_current_tau>
      </plugin>
  </gazebo>
  <gazebo>
      <plugin name="motherboard" filename="libLinearBatteryConsumerPlugin.so">
        <link_name>body</link_name>
        <battery_name>linear_battery</battery_name>
        <power_load>6.6</power_load> <!-- mother board power load = 6.6 W -->
      </plugin>
  </gazebo>

Any tip? thank you!