I haven't posted here in years but I did want to discuss this topic.
The Atmospheric Electric Circuit holds the Earth at Negative Charge. This means it has a limitless supply of free electrons.
Read about the Atmospheric Electric Circuit in this Richard Feynman Cal Tech University Lecture here:
https://www.feynmanlectures.caltech.edu/II_09.html
When you are in physical contact with the earth without insulators, immediately, your surface charge goes to Ground. The electrons slowly migrate through the skin at point of contact and through the gas exchange in the lungs (the upper respiratory tract is on the outside of the body so the Red Blood Cells take on the Ground Charge during the exchange and separate, more negative charge and repel. The phenomena is known as Zeta Potential).
For instance, if you have arthritis in the hands all you need to do is apply ground to the palm of the hand and arthritis will be eliminated in under 30 minutes. If you sleep with a carbon pillow case and carbon sleep mat plugged into ground (ground circuit) arthritis and inflammation in general will go away. Your sleep will greatly improve as the body calibrates with the change in voltage of the Earth that happens during the day regulating cortisol.
I've been a huge vitamin C advocate for years but three years ago I discovered the natural way to unlimited free electrons. My life has improved as well as anyone in my orbit who has followed my advice. I had to eliminate my Aunt's arthritic hand pain in less than 30 minutes for her to accept it but now she is permanently arthritis free (as long as she Grounds at night, issues will resurface if you stop Grounding).
Any kind of electrical device does not work correctly. Tennant is trying to make money from something that is FREE.
Many, many Earthing/Grounding studies can be found here:
https://earthinginstitute.net/research/