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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:

$Runtime (h) = Load (W) Capacity (Ah) \times Voltage (V) \times DoD \times Inverter Efficiency$

Example Calculation (LiFePO4):

$300 W 100 Ah \times 12 V \times 1.0 \times 0.95 = 3.8 hours$

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	$400 -$ 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

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:

$1 kW 4.8 kWh \times 0.95 = 4.56 hours$

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.

Edit by paco

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