Turn test data into clear efficiency metrics fast. Track amp-hours, watt-hours, and heat losses today. Export results, validate designs, and extend battery life safely.
| Scenario | V charge (V) | I charge (A) | t charge (h) | V discharge (V) | I discharge (A) | t discharge (h) | Energy efficiency |
|---|---|---|---|---|---|---|---|
| Lead-acid, moderate load | 14.4 | 10.0 | 2.50 | 12.0 | 8.0 | 2.80 | ~74.7% |
| Lithium, balanced cycle | 14.2 | 12.0 | 1.80 | 13.2 | 11.0 | 1.70 | ~86.1% |
| Cold weather, higher losses | 14.6 | 10.0 | 2.20 | 11.6 | 8.5 | 2.40 | ~64.9% |
Energy efficiency compares watt-hours out to watt-hours in across one cycle. Coulombic efficiency compares amp-hours out to amp-hours in. When energy efficiency is much lower than coulombic efficiency, voltage sag, internal resistance, and converter losses dominate. When both are low, side reactions, leakage, or measurement errors are likely. Track loss in watt-hours to estimate heat generation and validate design margins.
At 25°C, well-tuned lithium-ion packs often show 85–95% energy efficiency at 0.3–0.8C, while coulombic efficiency can exceed 99% in healthy cells. Lithium iron phosphate commonly performs similarly but with different voltage profiles. Flooded lead-acid systems frequently land around 70–85% energy efficiency, especially when charging includes absorption and float stages. AGM lead-acid can improve slightly at moderate rates. Real-world values depend on cutoff voltage, charge termination, balancing, and how averages are computed from logged data.
Resistive loss scales with I²R, so doubling current can quadruple heating. Longer operation at high current increases temperature, which raises resistance and reduces efficiency. For fair comparisons, keep the C-rate similar, use the same cutoff limits, and measure at ambient conditions. If your load is pulsed, compute averages or integrate data from a logger. Repeat at least three cycles and use the median result to reduce noise.
Cold conditions reduce ionic mobility and increase internal resistance, lowering discharge voltage and watt-hours out. Hot conditions reduce resistance but may increase side reactions, lowering coulombic efficiency and accelerating aging. A declining state of health reduces usable capacity and can increase polarization, so compare both percent efficiency and absolute watt-hours delivered. If efficiency drops after storage, check self-discharge and standby loads. Record temperature and notes so future tests remain comparable.
Use energy efficiency to size chargers, thermal paths, and input power budgets. Use coulombic efficiency to detect parasitic reactions, imbalance, or shunt errors. If loss percent rises over time at constant load, suspect higher impedance, loose connections, or cell degradation. If losses spike at higher current, consider thicker conductors, lower-Rds(on) switches, or active cooling. Export reports to build a trend history for maintenance planning.
Coulombic efficiency uses charge (Ah) and highlights side reactions or leakage. Energy efficiency uses energy (Wh) and also captures voltage drop, internal resistance, and conversion losses during charging and discharging.
Efficiency depends on actual operating voltage across the step. Using logged or measured average voltage captures sag, tapering, and cutoff behavior, which nominal ratings cannot represent accurately.
Yes. Use time-weighted averages from your logger, or integrate the data to compute Wh and Ah over the interval. Enter the resulting averages and total times for each step.
Common causes include rising internal resistance, degraded electrodes, poor connections, imbalance, and overheating. If coulombic efficiency stays high while energy efficiency drops, impedance is usually the main driver.
Values above 100% indicate incorrect inputs or averaging, such as mismatched time windows, voltage units, or current polarity. Recheck measurement intervals and ensure charge and discharge data come from comparable cycles.
Not always. Cold typically lowers efficiency by increasing resistance. Warm temperatures can improve voltage behavior short-term, but excessive heat increases side reactions and aging, which can reduce efficiency across repeated cycles.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.