As of my last knowledge update in September 2021, lithium-air (Li-Air) batteries are still largely in the experimental and research stage. There has been ongoing research to develop Li-Air batteries due to their potential for high energy density, but commercialization has not yet been achieved, and the specific voltage ratings for flexible Li-Air batteries may vary depending on the exact design and advancements in the field.
Traditionally, lithium-ion batteries (Li-ion) have a nominal voltage of around 3.7 to 3.8 volts. Li-Air batteries, in theory, could have higher energy densities, potentially leading to higher voltage ratings, but challenges related to stability, efficiency, and cycle life have hindered their practical implementation.
It's important to note that battery technology research evolves rapidly, and developments may have occurred since my last update. To get the most accurate and up-to-date information on the voltage rating of a typical flexible Li-Air battery, I recommend checking recent research publications or consulting experts in the field.