English: The number (log Y scale on the left) of patent families (solid lines) and of journal articles (dotted lines) related to lithium (metal and ion) batteries (green), fuel cells (magenta), vanadium flow batteries (blue), zinc-halogen batteries (red) vs the earliest priority (for patents) or publication (for journals) year. Certain political events (such as the launch of Sputnik 1 and Yom Kippur war), that affected research and development activity in alternative power sources, are shown as well. "1998 CARB" stands for zero-emission vehicle mandate by California Air Resources Board, which lead to the Hydrogen Economy Initiative. The black line is the inflation-adjusted oil-price (right Y axis, $/liter).