7 min. To push the boundaries of drone flight performance, batteries must become smaller and lighter. It appears that we reached a certain limit when it comes to power density. Lithium-Polymer (Li-Po) and Lithium-Ion (Li-ion) batteries have become very small and affordable, mainly driven by the mobile phone industry. This led to a wide adoption and today it is fair to say that the great majority of commercial unmanned aerial vehicles uses batteries as a power source (~96%).