Battery internal resistance varies significantly with both temperature and state of charge (SoC), and this behavior depends somewhat on the battery chemistry.
Influence of Temperature on Internal Resistance
- General trend: Internal resistance decreases as temperature increases. This is because higher temperatures improve the chemical reaction rates inside the battery, reducing resistive losses.
- Cold temperatures: At low temperatures, the internal resistance rises sharply. For example, lead-acid batteries can experience about a 50% increase in internal resistance when the temperature drops from +30°C to -18°C.
- This increase in resistance at low temperatures adversely affects both charging and discharging performances, causing slower charge acceptance and reduced discharge capabilities.
- The change in resistance with temperature is more pronounced at lower temperatures and becomes less steep as temperature rises.
Influence of State of Charge on Internal Resistance
- Lead-acid batteries: Internal resistance increases almost linearly with discharge due to the depletion and dilution of the electrolyte (specific gravity decreases). The difference in resistance between fully charged and fully discharged states is about 40%. Resistance levels are highest at low SoC and immediately after charging, with the lowest resistance typically occurring around half charge. Resting the battery for a few hours after charging reduces resistance by allowing electrochemical equilibrium (sulfation reversal).
- Lithium-ion batteries: Internal resistance changes less dramatically with SoC compared to lead-acid. It decreases asymptotically from about 270 milliohms at 0% SoC to roughly 250 milliohms at 70% SoC, with the largest changes happening between 0% and 30% SoC. The internal resistance is fairly flat from half to full charge.
- In both battery types, immediately after charging, the internal resistance is higher, and it improves (decreases) after a rest period.
Summary Table
| Factor | Lead-Acid Batteries | Lithium-Ion Batteries |
|---|---|---|
| Effect of Temperature | Resistance rises ~50% from +30°C to -18°C; lower temp → higher resistance | Resistance decreases as temperature rises; similar trend but varies with cell design |
| Effect of SoC | Resistance increases almost linearly as state of charge decreases; highest at low SoC and just after charging | Resistance is fairly flat from empty to full; largest decrease in resistance between 0–30% SoC |
| Resistance Change Magnitude | ~40% change between full charge and discharge | Small relative change, from ~270 mΩ at 0% to ~250 mΩ at 70% SoC |
This indicates that battery internal resistance is lowest at moderate temperatures and mid-range states of charge, and it increases notably at cold temperatures and very low SoC levels. The changes in internal resistance with temperature and SoC directly impact battery performance, including charge acceptance, discharge power, and overall efficiency.
Original article by NenPower, If reposted, please credit the source: https://nenpower.com/blog/how-does-battery-internal-resistance-change-with-temperature-and-state-of-charge/
