Meaning
Opposing electrochemical forces within a battery cell generate voltage drops when current flows through active materials and structural collectors. Measuring internal cell resistance provides a direct baseline for evaluating power delivery capability and thermal stability under load. Ohmic loss across internal electrolyte pathways and kinetic resistance at electrode interfaces combine to dictate total internal impedance.
High resistance values reduce output voltage during high-current discharge pulses, limiting peak power output. Thermal dissipation increases proportionally with the square of current multiplied by this internal opposition value.
Voltage Sag
Terminal voltage drops instantly when connected loads draw instantaneous surge currents from a pack. Excessive internal cell resistance causes severe voltage sags that trigger low-voltage system brownouts before battery capacity is exhausted. Integrated cellular modules and high-power radio transmitters demand high peak currents that amplify this voltage drop.
Selecting cells with low impedance keeps operating voltage above module reset thresholds during active transmission spikes.
Thermal Impact
Joule heating inside the cell enclosure accelerates electrolyte degradation during heavy discharge cycles. Increased internal cell resistance converts useful electrical energy into waste heat within the core structure. Elevated internal temperatures accelerate solid electrolyte interphase growth and worsen capacity retention over operational lifetime.
Thermal management designs must account for heat generated internally during high-rate discharge conditions.
Testing Method
Direct current pulse testing applies defined current steps to evaluate dynamic voltage responses under realistic operating loads. Characterizing internal cell resistance requires measuring the immediate step response alongside the slower electrochemical relaxation phase. Alternating current impedance spectroscopy provides detailed frequency-domain resolution of individual kinetic components.
Laboratory measurements must control ambient temperature precisely to ensure repeatable resistance baseline data.
