As of my last knowledge update in September 2021, flexible magnesium-ion batteries were still a relatively emerging technology, and specific details such as the exact voltage ratings of typical flexible magnesium-ion batteries might not be widely available or standardized. Research and development in battery technology continue to evolve, so there might have been advancements or changes since then.
Magnesium-ion batteries are being explored as a potential alternative to lithium-ion batteries due to the high energy density of magnesium and its abundance. However, the development of magnesium-ion batteries has presented challenges related to finding suitable electrolytes and electrode materials that can efficiently store and release magnesium ions.
For the most accurate and up-to-date information about the voltage rating of flexible magnesium-ion batteries, I recommend checking recent scientific literature, research articles, or news from reputable sources in the field of battery technology or materials science.