To date, evaluations of the energy efficiency of protocols and applications for small wireless devices have considered only the total energy utilization and ignored the dynamics of the battery itself.
This is true both for simulators and for platforms that measure energy consumption in real time . The battery is treated as a simple “bucket of mA-h”, which is depleted as various operations consume a given amount of current for a given amount of time.
In reality, a battery is a complex, non-linear electrochemical system. The way that charge is extracted from the battery affects how much of the nominal capacity can be used before the battery is depleted.
These effects have been extensively studied and modeled for many battery chemistries and structures, such as the Li-ion batteries used in mobile devices. This allows these systems to be specifically optimized for battery lifetime.
By contrast, very little data is available about the behavior of the cheap, non-rechargeable batteries that are typically used in small wireless devices.
Data is especially lacking about the behavior of these batteries under typical load patterns, with low duty cycles and relatively high peak currents, as for the operation of a transceiver or sensor/actuator.
As a result, it is simply not known to what extent battery effects should be taken into account when evaluating protocols and applications for such systems.
We describe a testbed for automated measurement of the discharge behavior of Li-coin cells, give some preliminary results, and discuss sources of experimental uncertainty. It is a work-in-progress testbed for studying how the energy performance of protocols and applications for small wireless devices is affected by battery discharge behavior.
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