Battery drain problem on mobile developement

I have made a ring toss game using Unreal on mobile device.

The game is running on fixed 30 fps and is using the Basic Lighting tier. The performance is and shader complexity is good on my iPhone6 S device (new).

However, after 10 minutes of play, the battery goes down like 10~15%. I have tried different devices and the issue is worse.

I have been searching online for battery saving solution but haven’t found many.

Is the battery issue related to the performance? CPU? GPU?

My question is what kind of area or tips I should look into to help the battery saving issue. Thanks!