Abstract-With the fast development in Internet and Mobile technologies, we are witnessing a proliferation of applications that support online collaborative group work. Such applications offer many advantages as compared to traditional web-based online collaborative learning, the most salient feature being the ability to work not only geographically distributed but also on the move, anytime and anywhere. Such applications in the very recent past used to offer lightweight client applications, leaving the burden of the application logics to the server side applications. However, as mobile devices are each time more powerful in terms of computing and storage capacity, client applications at mobile device are each time more complex and heavy so that members of the group could be able to work both offline and online, which arises when members of the group use smartphones and can eventually run out of Internet connection from time to time, or simply want to develop some activities locally. This comes to the price of wasting the battery in shorter time and thus impeding the collaborative work for longer time intervals. Due to this reason, researchers and developers are interested to develop sophisticated mobile applications under energy-aware requirements. In this work we analyse the energy efficiency of a group calendar that offers 1) information sharing among all of members of the group; 2) synchronisation among local calendars of members and global group calendar; 3) conflict resolution through a voting system; 4) awareness of changes in the entries (tasks, members, events, etc.) of the calendar and 5) sharing of calendars among different groups. In particular, we analyse the energy efficiency due to the synchronisations mechanisms employed by a group calendar as synchronisation is among most compute intensive and time consuming tasks. Our study sheds light on the need of implementing various synchronisation mechanisms from lightweight synchronisation to full synchronisation and their applications according to energy profile of the mobile device.