Im just wondering if the smart batteries that come with the dji fpv/fly more kit are compatible with other drones, since it looks like they use the same connector type (xt90?). Also trying to find out if the charger that comes with the dji fpv is compatible with other 6s batteries.

I'm pretty sure there are no other 6S batteries which are compatible with the DJI FPV charger. The balancing is done internally inside the battery. There's a communication line which allows the charger to communicate with the battery. I don't know how important this communication is while charging but the battery and drone must be able to communicate in order for the drone to fly.

Here's a thread where I show the inside of one of the batteries.

Hello there. Good day and thank you for reaching out. The DJI FPV Intelligent Flight Battery ( https://store.dji.com/product/dji-fpv-intelligent-flight-battery ) is only compatible with the DJI FPV Drone ( https://www.dji.com/dji-fpv?site=brandsite&from=nav ). The DJI FPV Intelligent Flight Battery provides up to approximately 20 minutes of flight time. Built-in intelligent battery management system. Thank you.