Aircard 815s (Unite Explore) Power down automatically

I want to keep the hotspot in the car and have it turn on and off with the car. If I remove the bettery, it seems to work for a while and then crash under load.

If I leave the battery in, it stays on and my devices connect while I'm in the house.

Do I need to use a bigger power supply in the car to power it without a battery? Is there a software solution?