When you charge and then discharge a battery cell you lose energy, the ratio of the amount of discharge to charge energy is the efficiency.
If we put 11 Wh into a battery cell when charging and recover 10 Wh when discharging the energy efficiency = 10 / 11 = 90.9%
Typical energy efficiencies:
- Lead acid ~70%
Also known as Faradaic Efficiency, this is the charge efficiency by which electrons are transferred in a battery. It is the ratio of the total charge extracted from the battery to the total charge input to the battery over a full cycle.
Coulombic efficiency values:
- Lead acid ~85%
- Lithium ion >99%
High coulombic efficiency usually indicates a long battery cycle life.
This is the ratio of the average discharge voltage to the average charge voltage over a cycle. The charging voltage is always higher than the rated voltage to activate the chemical reaction within the battery and hence losses.
- Vedran Bobanac, Hrvoje Basic, Hrvoje Pandzic, Determining Lithium-ion Battery One-way Energy Efficiencies: Influence of C-rate and Coulombic Losses, IEEE EUROCON-2021