I have flown with several 18650 cells in my carry on bags without issue. Use them for vape, flashlights, and battery banks. TSA never had a problem with them as long as I took them out and placed in tub with electronics. The nice thing is you can take a bunch of them with you and it won't exceed the capacity restrictions b/c they are not hooked together to create one battery. The last time I flew, I think I had at least 20 of them in my carry on. Got some funny looks, but wasn't even questioned. Maybe I just got lucky.
I have also taken a couple UV-5r HT's in my carryon without issue, TSA wanted batteries disconnected through the check, but no one cared if I reattached to the radios afterwards. I did take the antennas off though, just for easier packing.