This is an easy fix, to manage battery usage for the app, simply:
On iOS devices:
1. Launch iOS settings.
2. Find 'General.'
3. Select background App Refresh.
4. Either disable the feature entirely or specifically for Insight Timer.
On Android devices:
1. From the Home screen, tap the app slider, then open “Settings“.
2. Find Wireless and Networks.
3. Select “Data usage“.
4. Select the app you want to limit background data on.
5. Toggle “Background data” to “On” or “Off” as desired.