Battery knowledge · Units and electrical basics
Ohm
The SI unit of electrical resistance: one volt per ampere. Cell internal resistance is about a milliohm for a large automotive cell and tens of milliohms for a small cylindrical one. [1]
- Abbreviation
- Ω
- Unit
- Ω
Example
Voltage under load
5 A through 20 mΩ gives 0.1 V ohmic drop.
Chosen OCV curve; no chemistry calibration, hysteresis or voltage cutoff.
Explore the graph
Discharge current creates an ohmic drop below open-circuit voltage.
5 A through 20 mΩ gives 0.1 V ohmic drop.
V_terminal = OCV − I_discharge R
Illustrative model. Chosen OCV curve; no chemistry calibration, hysteresis or voltage cutoff.
Use in Lemonergy
Lemonergy Studio blocks
Relate current and voltage
Conserving components solve constitutive relations and node balance.
Blocks to use
- Controlled voltage source
Supplies voltage
Inputs & settings
- voltageV
- Resistor
Relates current and voltage
Inputs & settings
- resistanceOhm
- 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.
Example. A 1 V drop across 2 Ω implies 0.5 A.
Observe. Topology sets individual element voltages.
The RC example includes a capacitor: transient current varies and source voltage is not always resistor voltage.
Open the electrical circuit →References & further reading
Technical references
- The International System of Units (SI), 9th edition
Bureau International des Poids et Mesures · 2026
Technical reference · Definitions of SI units and coherent derived units; 2026 revision.