Battery doesnt like

I live for this app. This, in the classroom, is the next best thing to having a Harmony Director. The only downside is the extreme battery drain on the device. I have an iPhone 7 and this battery can last all day with heavy use, but whenever I open Tonal Energy, I can be on it for a few minutes and be down 10-20%. This is too bad, because this app is a must have for any music teacher. Also Ive heard many people say sound on Bluetooth is different. Not sure if this is a hardware or software issue.

Bryant S about TonalEnergy Tuner & Metronome, v1.4.2