I went with a portable battery, https://www.amazon.com/dp/B0CXDXP8VR. I keep it in the case plugged into the 3 battery charger. Charging up all 3 batteries one time will exhaust the portable one from 100%. In theory you could keep it plugged into...
I really, just me personally, find pre-cut foam cases a waste of money. If you upgrade of sell your drone, they have few alternative uses and the foam will not fit anything else. They do not really increase the sale price of your drone in the end...