Always use the Karma charging unit for the Controller, Drone Battery and the Karma Grip. This unit is designed for that purpose. Also charge from a 100 -240 volt alternating source and not from a USB port.
Along these same lines...I thought I would forgo the use of the Karma charging unit as I was charging the Karma Grip in-between destinations on a recent road trip. Instead, I used a USB-C cable attached to my car's DC outlet. BAD IDEA!!!
My Gopro Karma stopped working just as I reached Glacier Point in the Scenic Yosemite National Park. Several attempts at re-calibration and hard reset did not correct the problem. I eventually took the camera out of the harness, and just did the best I could, without the benefit of the Grip. Fortunately, it was close to the end of the day...and I have been there several times before, but I couldn't imagine how upset I would have been if that was a "once in a lifetime" trip, especially given how beautiful that particular spot is for filming.
Eventually, when I got back to the hotel, I plugged the Karma Grip in overnight, and the following day it worked fine. Honestly, I was expecting the worst!
Alternatively, Had I just left things well enough alone, my battery probably would have lasted for the rest of the day. I had the Karma charger with me, and I could have just plugged it into the AC outlet in my car. In the past, I have also used the charger in combination with the Karma Batteries when I am hiking to charge the Karma Grip on longer hikes. It is a bit of extra weight...but worth the consideration on scenic hikes.