Battery knowledge · Capacity, energy, power and ratings
Coulombic efficiency
Charge delivered on discharge divided by charge put in on the previous charge. A healthy lithium-ion cell exceeds 99.9 %; the missing fraction is lithium lost to side reactions, so CE is an early and sensitive aging signal.
- Abbreviation
- CE
- Unit
- %
- Relationship
- CE = Q_discharge / Q_charge
Example
Compare charge in and charge out
If a defined test charges 5.00 Ah and subsequently discharges 4.95 Ah over the chosen voltage window, its coulombic efficiency is 99%. This ratio alone does not include voltage-related energy loss.
Explore the graph
Returning most of the charge does not return the same fraction of energy.
99% × 92% = 91.08% energy efficiency.
η_energy = η_charge × V̄_discharge / V̄_charge
Illustrative model. Matched cycle and measurement boundaries; auxiliary loads omitted.
Use in Lemonergy
Lemonergy Studio blocks
Connect SOC and voltage
The battery integrates charge and combines OCV with resistance.
Blocks to use
- Battery with SOC-dependent OCV
Stores charge and supplies terminal voltage
Inputs & settings
- capacityAh
- initialSoc
- emptyVoltageV / fullVoltageV
- resistanceOhm
- Electrical ports p and n
- Regulated CC/CV charger
Regulates current and voltage
Inputs & settings
- currentA
- voltageV
- cutoffCurrentA / cutoffHoldS
- Electrical ports p and n
- Electrical reference
Sets zero potential
Inputs & settings
- Connect p to reference net
This overview identifies the components to use. Follow the example in Lemonergy for their connections and settings.
- Inspect capacity, initial SOC and OCV endpoints.
- Compare OCV with terminal voltage.
Example. OCV endpoints of 300 and 420 V give 360 V at 50% SOC. Charging at 10 A through 0.08 Ω adds 0.8 V.
Observe. At unity coulombic efficiency, 10 A for 1 h adds ten percentage points to 100 Ah.
Internal model SOC is not an estimate of an unknown physical battery. OCV is linear and resistance fixed.
Open the Studio example →References & further reading
Further reading on this topic
These sources provide broader context; they are not presented as citations for every statement in this entry.
- The International System of Units (SI), 9th edition
Bureau International des Poids et Mesures · 2026
Topic background · Definitions of SI units and coherent derived units; 2026 revision.
- Battery Test Manual For Electric Vehicles, Revision 3
Jon P. Christopherson · Idaho National Laboratory · 2015
Topic background · Performance characterization, pulse resistance/power, life testing and reference performance tests; historical 2015 edition.