Why Lithium-ion Battery Voltages Have Decimal Points?

You may find it odd that lead-acid battery voltages come in neat whole numbers like 12V, 24V, 36V, while lithium-ion batteries have voltages like 12.8V, 25.6V, 38.4V. It seems non-standard and would annoy any perfectionists! However, there is a material science reason for this. 

Batteries achieve their voltages through individual cells connected in series and/or parallel. The battery voltage must therefore be a multiple of the single cell voltage. For lead-acid batteries, the nominal voltage of a single cell is 2V. 

However, the nominal voltage of a single lithium-ion cell is 3.2V. This voltage level is determined by the electrochemical properties and potential difference between the positive and negative electrode materials, not the quantity or shape of the materials. A single lead-acid cell will always be around 2V, and a single lithium-ion cell will always be around 3.2V.

To create a 12V lead-acid battery, six 2V cells are connected in series, giving 6 x 2V = 12V. This became the standard voltage for automotive and many other applications. 

Lithium-ion batteries aim to directly replace lead-acid batteries at their common voltage ratings. So to achieve the equivalent of a 12V battery, manufacturers connect four 3.2V lithium-ion cells in series. 4 x 3.2V gives the familiar 12.8V output - close enough to 12V to use the same applications and wiring, while utilizing the higher energy density lithium-ion chemistry.

Therefore, in summary - the decimal points in lithium-ion voltages result from the fixed 3.2V single-cell chemistry, whereas lead-acid batteries conveniently have 2V cells to give simple whole number pack voltages. Material science, not aesthetics, determines battery voltages.

If you need to purchase lithium batteries, please visit the product page for more information.