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Only certain battery voltages exist, because this voltage depends intrinscally on the battery's chemical composition. (CC BY-SA) has a very good summary list, reordered from lowest to highest voltage:
Battery Shape Chemistry Nominal Voltage Rechargeable?
AA, AAA, C, D (Rechargeable) NiMH or NiCd 1.2V Yes
AA, AAA, C, and D Alkaline or Zinc-carbon 1.5V No
Coin Cell Lithium 3V No
Silver Flat Pack Lithium Polymer (LiPo) 3.7V Yes
9V Alkaline or Zinc-carbon 9V No
Car Battery Six-cell lead acid 12.6V Yes