From an article (paywalled) in the Washington Post on the same process:
The process described by the Texas A&M team exploits the natural ability of battery-like mitochondria to transfer from one cell to another.
“We are supercharging stem cells so that they can donate these batteries to damaged cells at a much higher rate,” Gaharwar said.
The stem cells, he said, “have a homing ability. Whenever they see damage, they go and settle down over there and they basically try to regenerate the damaged area.”
Scientists carried out the procedure using different cell types in a lab dish. Gaharwar said he and his colleagues hope to begin testing the technique in rats in January or February.
This seems to me an “easy” path to the fountain of youth,. We already have millions of very smart stem cells in our body wanting to rejuvenate us, its what they’re made to do, its their purpose in life, so we just need to give them a helping hand (or a spare battery)