How many hours will a 12V 100Ah battery last?
A 12V 100Ah battery lasts 5–10 hours depending on load. At a 100W draw, runtime is ~10 hours (1200Wh ÷ 100W), but real-world factors like Depth of Discharge (DoD) (50% for lead-acid, 80% for lithium) and inverter efficiency (~85%) reduce this. For example, powering a 600W system with lead-acid: (100Ah × 12V × 50% DoD) ÷ 600W ≈ 1 hour. Always size batteries 20% above calculated needs.
How is battery capacity calculated?
Battery capacity (Wh) = Voltage (V) × Amp-hours (Ah). A 12V 100Ah battery stores 1,200Wh. Actual usable energy depends on DoD—lead-acid typically allows 50% discharge, yielding 600Wh. Lithium variants (LiFePO4) permit 80% discharge, offering 960Wh. Pro Tip: Multiply Wh by 0.85 to account for inverter losses.
Battery runtime hinges on dividing usable energy by load power. For example, a 1,200Wh lead-acid battery powering a 200W fridge: (1,200Wh × 50% DoD) ÷ 200W = 3 hours. But what if ambient temperatures drop below 10°C? Cold reduces lead-acid efficiency by 20–30%, slashing runtime further. Lithium batteries handle cold better, losing only 10–15% capacity at 0°C. Always check discharge curves for your battery type.
What factors affect battery runtime?
Load power, DoD limits, and temperature dictate runtime. High-drain devices (e.g., inverters) reduce efficiency, while lithium batteries outperform lead-acid in partial cycling. Lead-acid loses 20% capacity yearly even unused.
Practically speaking, a 12V 100Ah lead-acid battery powering a 500W inverter might last (1,200Wh × 50% × 85% efficiency) ÷ 500W = 1.02 hours. But what if you’re running multiple devices? A 100W TV + 200W fridge + 50W lights = 350W total, extending runtime to ~1.7 hours. Pro Tip: Use lithium batteries for cyclic applications—they maintain 80% capacity after 2,000 cycles vs. lead-acid’s 300–500.
| Factor | Lead-Acid Impact | Lithium Impact |
|---|---|---|
| DoD | 50% (600Wh) | 80% (960Wh) |
| Cycle Life | 300–500 | 2,000–5,000 |
| Cold (0°C) | 30% loss | 15% loss |
Lead-acid vs. lithium: Which lasts longer?
Lithium batteries (LiFePO4) deliver 3–5x longer lifespan than lead-acid. They support deeper discharges (80% vs. 50%) and retain capacity better over time.
For instance, a 12V 100Ah lithium battery powering a 150W load daily would last (960Wh ÷ 150W) ≈ 6.4 hours per cycle. Over 2,000 cycles, that’s 12,800 hours total. A lead-acid counterpart provides (600Wh ÷ 150W) ≈ 4 hours for 500 cycles, totaling 2,000 hours—84% less. Beyond cost, lithium’s weight (15–20kg vs. 25–30kg for lead-acid) simplifies installation. Pro Tip: For solar setups, lithium’s faster charging (1–2 hours at 50A) outperforms lead-acid’s 8–10-hour absorption phase.
How to calculate runtime for specific devices?
Use: Runtime (hours) = (Battery Wh × DoD × Inverter Efficiency) ÷ Device Wattage. For a 12V 100Ah battery running a 60W TV via 90% efficient inverter: (1,200 × 0.5 × 0.9) ÷ 60 = 9 hours.
But what if your TV has startup surges? Lead-acid handles 3x surges briefly; lithium manages 5x. For a 60W TV with 180W surge: ensure inverter surge rating exceeds 180W. Real-world example: A 12V 100Ah lithium battery running a 120W gaming PC via 85% efficient inverter: (960Wh × 0.85) ÷ 120W ≈ 6.8 hours. Transitional tip: Always derate calculated runtime by 15% for aging batteries.
| Device | Wattage | Runtime (Lead-Acid) |
|---|---|---|
| LED Lights | 20W | 30 hours |
| Fridge | 150W | 4 hours |
| Microwave | 1,000W | 0.6 hours |
Does inverter efficiency affect runtime?
Yes—inverters waste 10–15% energy as heat. A 1,200Wh battery with 85% efficient inverter delivers 1,020Wh. For lithium: 960Wh × 0.85 = 816Wh usable.
For example, a 12V 100Ah lead-acid battery powering a 300W device: (600Wh × 0.85) ÷ 300W ≈ 1.7 hours. Upgrade to a 95% efficient inverter: (600 × 0.95) ÷ 300 = 1.9 hours—12% longer. Pro Tip: Pure sine wave inverters are 5–10% more efficient than modified sine wave for sensitive electronics.
How to extend battery life?
Keep lead-acid above 50% charge and lithium above 20%. Store at 50–80% charge in 15–25°C environments. Use compatible chargers.
For lead-acid, equalize charges every 30 cycles to prevent sulfation. Lithium batteries need balancing every 10 cycles. Example: A 12V 100Ah battery bank stored at 100% charge for 6 months loses 20–30% capacity. Transitional tip: Install temperature sensors—charging below 0°C damages lithium cells.
RackBattery Expert Insight
FAQs
Yes, but only briefly: (1,200Wh × 50% DoD × 85% efficiency) ÷ 1,000W ≈ 0.5 hours. Use lithium for higher surge tolerance.
Is a 12V 100Ah battery suitable for cars?
No—cars need cranking batteries (CCA rating). Deep-cycle 12V 100Ah batteries are for RVs/solar, not engine starts.
How long to recharge a 12V 100Ah battery?
With a 10A charger: 10 hours (100Ah ÷ 10A). Lithium charges 2x faster (20A) for 5-hour full cycles.