In addition to Christina's guidance, the DD app will turn the battery level icon red when it reaches 30%. In addition to that, a small pop-up will display at the bottom of the screen at each 1% drop below 30.
In DJI Go4, I have my battery warning level set at 20% and critical at 10%. That doesn't mean that I will allow it to get that low. When flying a DD mission that is going to take most of a battery or possibly more than 1, I compare the remaining percentage to what is left to fly. If the mission is going to end very close to the take off/landing point, I will let it get lower than if the ending waypoint is far away. Likewise if the mission is going to take more than 1 battery, I will choose at which waypoint I abandon the mission by tapping the GO Home icon. DD will continue the mission starting at the last waypoint reached so I consider all of these factors when I decide to bring the aircraft home.
I would advise you to take control of your flights, whether in DD or any other control app and monitor the fuel (battery) level and terminate the flight when appropriate for the conditions.
If you fall unconscious during a mission, then go ahead and rely on DJI to act on the battery level (sarcasm). But otherwise, don't delegate critical operational decisions to automation if you can help it.
Just friendly advice. Take it or leave it !