How Long Does a 100Ah Battery Last?
Selecting the right battery and accurately predicting its runtime is critical for applications ranging from renewable energy systems to marine and RV use. This guide provides a technical breakdown of 100Ah battery performance, including capacity calculations, chemistry comparisons, and real-world runtime adjustments.
Understanding Battery Capacity: Amp-Hours (Ah) and Energy Density
Battery capacity, measured in amp-hours (Ah), quantifies the total charge a battery can deliver at a specific voltage. A 100Ah battery provides:
- 100A for 1 hour (at 12V = 1.2kWh)
- 20A for 5 hours (Peukert’s Law adjustments apply for lead-acid under high discharge).
Key Formula:
Runtime (h)=Capacity (Ah)×Voltage (V)×DoD×Inverter EfficiencyLoad (W)Runtime (h)=Load (W)Capacity (Ah)×Voltage (V)×DoD×Inverter Efficiency
Example Calculation (LiFePO4):
100Ah×12V×1.0×0.95300W=3.8 hours300W100Ah×12V×1.0×0.95=3.8 hours
Chemistry Comparison: LiFePO4 vs. Lithium-Ion vs. Lead-Acid
| Parameter | LiFePO4 | Lithium-Ion | Lead-Acid |
|---|---|---|---|
| Energy Density | 120-160 Wh/kg | 150-200 Wh/kg | 30-50 Wh/kg |
| Cycle Life | 2,000-5,000 cycles | 500-1,500 cycles | 300-500 cycles |
| DoD | 100% | 80-90% | 50% |
| Temp Range | -20°C to 60°C | 0°C to 45°C | -20°C to 50°C |
| Cost per kWh | 400−400−600 | 300−300−500 | 100−100−200 |
Applications:
- LiFePO4: Solar storage, EVs (safety & longevity).
- Lithium-Ion: Consumer electronics (high energy density).
- Lead-Acid: Backup power, automotive (low cost).
Runtime Adjustments: Real-World Factors
- Temperature Effects:
- Cold (<0°C): Lithium batteries lose 20-30% capacity; lead-acid drops 50%.
- Heat (>40°C): Accelerates degradation in all chemistries.
- Depth of Discharge (DoD):
- Discharging LiFePO4 to 100% DoD yields ~3,800 cycles vs. 1,200 cycles at 80% DoD.
- Inverter Losses:
- Assume 85-95% efficiency for DC-AC conversion.
Practical Runtime Scenarios
| Application | Load (W) | LiFePO4 (h) | Lead-Acid (h) |
|---|---|---|---|
| RV Refrigerator | 150 | 7.6 | 2.8 |
| Off-Grid Solar | 500 | 2.3 | 0.8 |
| Golf Cart (Hills) | 800 | 1.4 | 0.5 |
Golf Cart Case Study:
A 100Ah LiFePO4 battery lasts 4-6 hours on hilly terrain (25mph, 800W load), while lead-acid lasts 1.5-2 hours.
Parallel Configurations: Extending Capacity
Wiring four 12V 100Ah LiFePO4 batteries in parallel yields 400Ah @ 12V (4.8kWh). Powering a 1,000W load:
4.8kWh×0.951kW=4.56 hours1kW4.8kWh×0.95=4.56 hours
Critical Notes:
- Balance parallel connections to prevent uneven discharge.
- Use a Battery Management System (BMS) for lithium arrays.
Conclusion
A 100Ah LiFePO4 battery outperforms lead-acid by 3-4x in runtime and lifespan, particularly in high-demand applications. Always factor in DoD, temperature, and inverter losses for accurate predictions. For systems requiring >5kWh, consider 48V LiFePO4 banks to reduce current and minimize losses.