  The Age of Information (AoI) is an end-to-end metric frequently used to
understand how "fresh" the information about a remote system is. In this paper,
we present an experimental study of the relationship between AoI and the energy
spent by the device that produces information, e.g. an IoT device or a
monitoring sensor. Such a relationship has been almost neglected so far, but it
is particularly important whenever the sensing side is battery-operated. The
study is carried out in a scenario where access is achieved via the cellular
network and information is transferred using MQTT, a popular messaging protocol
in the IoT domain. Numerous parameters of operation are considered, and the
most efficient solutions in all configurations are provided.
