"Traditionally, aircraft power system use passive power converter coupled with NiCad battery to provide power to 28Vdc buses from main AC network. This solution is very mature, but power quality from this architecture is low and impact avionics loads designs and overall system reliability.Recent progress in power electronics and lithium –ion batteries allows higher power density compared to traditional passive approach. The new solutions allow considerable performances enhancement and weight/volume savings (feeder, loads…) and better reliability at aircraft level.Management of lithium battery charge and discharge imposes multiples protections in order to insure a proper behavior during all possible scenarios and to ensure safety, even during abusive conditions. No break power transfer coordination is also a challenge at architecture level.The main objectives of this study is to optimization the ratio weight / volume (at system level) of active power conversion system coupled with li-ion energy storage, including mutualisation of function such as battery charger and TRU. This optimisation will also improve battery expected life, keeping the functionality of a no break Power transfer 28Vdc.In addition, this project can demonstrate benefits of a modular battery system concept, combining battery modules to subsystems and systems on demand. This leads to a high flexibility and interchange ability of battery modules."