Active materials in batteries suffer from deleterious chemical and structural evolutions during cycling. To follow these modifications, transmission electron microscopy and associated techniques (EELS, EDX) are of great use. However, these materials can undergo drastic changes under the electron beam. In this study the various microstructural and chemical evolutions induced by electron irradiation were thoroughly investigated at different charging states on a MnO material reacting through the conversion process leading to nanoparticles. During the electron irradiation, compounds pulverization, nanograins growth as well as the formation of manganese carbide were observed. Consequently, knowing the modifications the sample can undergo under electron irradiation and managing to the best the TEM parameters (spot size, aperture size...) to limit its effect can be of help to avoid misinterpretation and to fully understand the mechanisms, which occur during cycling. (C) The Author(s) 2017. Published by ECS. All rights reserved.