I have this same drone, but have never had that issue, if you have knowledge about repairing electronics and feel comfortable, i would try opening it up and checking the battery connection wires, that may have gotten unplugged somehow. If that doesnt work i would recommend either a battery replacement (i don't know if that is possible to do DIY for this controller) or i would send it back to DJI and see if they can repair it. A sudden loss of power may not be a battery related issue as batteries dont tend to do that if they are connected properly, so it may also be a problem with some other part of the controller or power distribution circuitry inside.