Battery is not explicitly considered when saving/querying the VideoPerfHistory that backs MediaCapabilities. We expect performance to be affected when on battery power (e.g. cpu throttling), so we should consider using battery alongside other stream properties (resoluiton, fps, etc) to index video performance stats in the DB. 

The quick way to evaluate priority/effect of this work is to start including battery status in the UKM metrics. We can then determine how significant the performance impact and how it affects prediction accuracy. The two may be correlated, but don't have to be.