How many hours can a 100Ah battery last?
A 100Ah battery’s runtime depends on connected load and system voltage. At 12V, a 100Ah battery theoretically delivers 1.2kWh (100Ah × 12V). Dividing this by appliance wattage gives runtime hours—e.g., a 100W device draws ~8.3A (100W/12V), lasting ~12 hours (100Ah/8.3A). Real-world factors like depth of discharge (80% for lithium) and inverter efficiency (~85%) reduce this by 30-40%.
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How is battery runtime calculated?
Runtime uses Ah rating and load current: Hours = 100Ah / Load (A). For 240W AC devices at 12V, factor in inverter losses. Pro Tip: Multiply Ah by voltage first (12V×100Ah=1.2kWh) before dividing by appliance watts for accurate estimates.
Practically speaking, a 100Ah lithium battery powering a 50W fridge would theoretically last 24 hours (1200Wh/50W). However, depth of discharge (DoD) limits usable capacity—80% for LiFePO4 gives 960Wh. Inverter inefficiency (15% loss) further reduces this to ~816Wh, yielding ~16.3 hours. For DC loads like LED lights (10W), skip the inverter, achieving 96Ah/0.83A= ~115 hours. Real-world example: A 100Ah battery runs a 200W TV for 4.8 hours (960Wh/200W) with inverter. Warning: Avoid continuous loads exceeding 50A—100Ah batteries typically have 100A max discharge rates.
What factors reduce battery runtime?
Temperature, aging, and charge cycles degrade capacity. Lithium batteries lose 2-3% capacity yearly; lead-acid degrades 30% faster in sub-zero temps.
Beyond basic calculations, ambient temperature critically impacts performance. At -20°C, lead-acid batteries deliver just 50% capacity, while lithium variants maintain ~80%. Battery age also matters—after 500 cycles, a LiFePO4 cell retains 80% capacity, reducing runtime proportionally. High discharge rates induce voltage sag, too: pulling 50A from a 100Ah battery may drop voltage to 11V, effectively cutting capacity by 15%. Pro Tip: Use battery heaters in cold climates to preserve lithium-ion efficiency. For example, an unheated 100Ah AGM battery powering a 150W heater at -10°C lasts only 3 hours versus 6.5 hours at 25°C.
| Factor | Lead-Acid Impact | Lithium Impact |
|---|---|---|
| Low Temp (0°C) | -50% Capacity | -20% Capacity |
| 100% DoD Cycles | 300-500 | 2000-4000 |
| Peak Discharge Rate | 50A (5C) | 100A (1C) |
Why does voltage matter in runtime?
Higher voltage systems reduce current draw for same power, extending runtime. A 48V 100Ah battery (4.8kWh) lasts 4x longer than 12V at equivalent wattage.
Consider this: A 1000W load at 12V pulls 83.3A (1000W/12V), draining a 100Ah battery in ~1 hour (factoring 80% DoD). The same load at 48V draws only 20.8A, allowing 4.8 hours runtime. This principle explains why EVs use 400-800V systems—lower current reduces heat and wiring costs. Pro Tip: For solar systems, 48V configurations minimize energy loss over long wire runs. A 48V 100Ah lithium battery running a 500W inverter can power a laptop (60W) for 64 hours (4800Wh × 80% DoD / 60W). But what if you mix voltages? Never connect 12V and 48V batteries in series without a balancer—voltage mismatch causes dangerous imbalances.
How do real-world applications affect runtime?
Intermittent vs. continuous loads alter consumption. A 100Ah battery lasts 10 hours with a 10A intermittent load (e.g., lights) but just 8 hours with continuous 12A (e.g., CPAP machine).
Take solar-powered security cameras: drawing 0.5A during daylight (solar charging) and 2A at night. Over 24h, total consumption is (14h×0.5A)+(10h×2A)=27Ah, allowing ~3.7 days runtime. Comparatively, a medical oxygen concentrator running 24/7 at 5A would drain the battery in 16 hours (100Ah/5A × 80% DoD). Pro Tip: Use lithium batteries for cyclic applications—they handle deeper discharges without sulfation. For example, a lead-acid battery cycled daily to 50% DoD lasts 2 years, whereas LiFePO4 under same use lasts 10+ years.
| Application | Load (W) | Runtime (h) |
|---|---|---|
| RV Refrigerator | 80 | 12 |
| Drone Charger | 300 | 3.2 |
| CPAP Machine | 60 | 16 |
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FAQs
Can a 100Ah battery run a 2000W inverter?
Briefly, but not sustainably. A 2000W load at 12V requires 166A—exceeding most 100Ah batteries’ 100A discharge limit. Expect BMS shutdowns within minutes.
How long will a 100Ah battery last with a 500W load?
At 12V: 500W/12V=41.6A. Usable capacity=80Ah (80% DoD). Runtime=80Ah/41.6A≈1.92 hours. With 85% inverter efficiency: ~1.63 hours.
Does connecting two 100Ah batteries double runtime?
In parallel (12V): Yes—200Ah capacity. In series (24V): Same energy (1200Wh), but higher voltage reduces current draw for same power, improving efficiency.