A technology has been developed for the extreme miniaturization of lithium ion micro batteries using wafer level processing. These batteries will be used as electronic buffer storage in future miniaturized sensor nodes, data loggers, RFID devices and medical applications. The micro batteries can store the energy generated by energy harvesters which are a prerequisite for energy autarkic wireless sensor nodes and enable the technology for ambient intelligence and the internet of things. Between 2000 and 10000 micro batteries can be fabricated on one 300 mm wafer, being a low cost process. Process optimization of silicon processing was necessary to define cavities for the electrochemical electrodes, current collectors and contacts. The active masses are applied by means of dispensing. Technology development was required to optimize the electrode pastes and electrolyte for application in micro channel structures. Thus a wide variety of state of the art electrode materials can be used and the battery parameters can be tailored according to their application. A novel battery design was tested with anode and cathode fabricated side by side in a planar arrangement. Electrode width and depth as well as electrolyte thickness are the main design parameters to achieve sufficient current capability which is required for wireless sensor nodes.