Internal resistance refers to the opposition a battery presents to current flow, converting electrical energy into heat during charge/discharge cycles. Measured in milliohms (mΩ), this value varies with factors like temperature, state-of-charge (SOC), and battery chemistry.
For instance, healthy lithium-ion cells typically maintain resistances below 20 mΩ, while alkaline batteries may exceed 100 mΩ even when new. Higher resistance accelerates capacity fade, reduces usable energy, and increases thermal runaway risks, particularly in high-drain applications like EVs and grid storage.
Key efficiency metrics linked to resistance include:
• Energy Density Loss: Every 10 mΩ increase in resistance reduces usable capacity by 3-5% in 18650 cells.
• Voltage Sag: Pulses exceeding 3C discharge rates can cause voltage drops of 15-20% in aging Ni-MH batteries.
• Cycle Life Degradation: Cells with resistance doubling initial values often reach end-of-life (80% capacity) 30% sooner.