RISC-V chips so far have been significantly lower-area and higher efficiency than their closest ARM counterparts, when on the same fabrication process. This has held true for embedded microcontrollers and lower-end application processors. And RISC-V with the newly standardized extensions and Rva-22 profiles seems to have even more potential at the higher end. It obviously won't make a huge difference to battery life, but it shouldn't hurt either.