I've been conducting some tests, comparing the power consumption of Spotify and Deezer on iOS. My findings are that
streaming music on Deezer can last up to twice as long as Spotify on a single battery charge.
My test were done on both an 6. gen iPod Touch and an iPad Air 2, both running the latest iOS version, screen turned off, wifi enabled and streaming quality set to the highest lossy settings.
For example, on my iPod touch I easily can stream music for over 32 hours before the battery runs dry. But Spotify barely manages to give me 16 hours under comparable conditions.
How is that even possible? My guess this is caused by the different audio codecs (mp3 vs. ogg vobis) both services use. Because ogg vobis is not natively supported by the chips on iOS devices, everything has to be done through software. This might explain the stark differences in battery life between the two.
My suggestion would be to switch the audio codec on iOS to mp3 or aac.