# Coloumbic Efficiency

From Open Electrical

The coloumbic efficiency of a battery is defined as follows:

- [math] \eta_{c} = \frac{Q_{out}}{Q_{in}}\, [/math]

Where [math] \eta_{c} \, [/math] is the coloumbic efficiency (pu)

- [math] Q_{out} \, [/math] is the amount of charge that exits the battery during the discharge cycle (C)
- [math] Q_{in} \, [/math] is the amount of charge that enters the battery during the charging cycle (C)

Coloumbic efficiency is not 100% because of losses in charge, largely because of secondary reactions, such as the electrolysis of water or other redox reactions in the battery. The coulombic efficiency of a typical lead-acid battery is >95%.