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Home > Blog>100Ah Battery Runtime Decoded: Expert Calculations for Lithium, LiFePO4 & Lead-Acid

How Long Does a 100Ah Battery Last? In-Depth Analysis & Runtime Charts

 

12V 100Ah lifepo4 battery

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)

Example Calculation (LiFePO4):

100Ah×12V×1.0×0.95300W=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 400−600 300−500 100−200

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

  1. Temperature Effects:

    • Cold (<0°C): Lithium batteries lose 20-30% capacity; lead-acid drops 50%.

    • Heat (>40°C): Accelerates degradation in all chemistries.

  2. Depth of Discharge (DoD):

    • Discharging LiFePO4 to 100% DoD yields ~3,800 cycles vs. 1,200 cycles at 80% DoD.

  3. 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 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.


Edit by paco

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