You can manage your battery with an intelligent system when your battery is running low, this feature will help you maintain a connected state.
Here is an article introducing S Power Planning and how to use the feature on the Galaxy J7 Prime for your reference:
I. Introduction to S Power Planning.
S Power Planning provides you with an intuitive battery management system that understands your needs when your device is low on battery. It allows you to receive calls, maintain connectivity for calls, messages, or call forwarding when your device is out of battery.

1. Reserve Battery for calls allows you to save battery for important data with a reserve battery mode. It lets you keep a certain percentage of battery reserved for calls and messages by turning off background apps and activities.
2. Extend battery time allows you to set 3 different levels based on your phone usage pattern. Each level describes a number of hours until the phone powers back on.
3. Forward calls when no battery With call forwarding, you get an option to forward your calls to another number in case your phone runs out of battery.
Step 1: Swipe down the notification bar > Select S Power Planning.

Step 2: Select Allow.

Step 3: Choose the features you want to enable > Select enable.

You can also refer to 'How to turn on LED notification light for missed calls on Samsung J7 Prime'.
