# Is the $C$ rating of a battery a measure of Capicitance or Charge?

I have become confused as to the meaning of what a C rating of a battery means. My understanding is that because a C rating is measured in milli-ampere hours the units should cancel to be a unit of charge. However, sources such as A Guide to Understanding Battery Specifications (Paragraph 3), and This physics stack exchange post seem to indicate that a $C$ rating is a unit of capacitance which is of course measured in Coulombs per Volt.

I my question is what a $C$ rating really is and if there is a more intuitive interpretation.

$1~\textrm{Ampere-hour}$ equals $3600~\textrm{Coulomb}$ of charge.
The voltage on a battery is also almost constant (if it's too high or too low, the electrochemical system in it will usually degrade very quickly). We therefore measure the "capacity" of a battery with a single amount of charge, with the SI units of Coulomb, however, technically the easier to handle quantity is $1\rm mAh=3.6~ Coulomb$ or $\rm Ah=3600~Coulomb$. This will immediately tell us the necessary charge current, if we are, for instance, charging at $\rm C/10$.
For example: if the battery has $12~\rm Ah$ of capacity, then the charging current has to be $1.2~\rm A$ at $\rm C/10$. For many batteries the specified charging time is $14~\rm h$ to make up for the inefficiency of the charging process because not all charge that we send trough the battery is actually used to perform a chemical conversion of one ion species into another.
In comparison the capacitance of a capacitor is constant and the amount of charge it can hold is proportional to the voltage between its terminals, which can be anything between 0 and the max. operating voltage, which is usually limited by dielectric breakdown of its dielectric. Because of this proportionality we specify the capacitance of a capacitor in $\rm [Farad]=[Coulomb/V]$, a unit that doesn't make sense for batteries, because the voltage on a battery can't be changed.