To calculate how long a 200Ah battery will last, use the formula: Runtime (hours) = Battery Capacity (Ah) ÷ Load Current (A). For example, a 12V 200Ah battery powering a 10A device provides ~20 hours theoretically. If using power (Watts) instead of current, first calculate energy: Battery Energy (Wh) = Voltage (V) × Capacity (Ah), then divide by load power: 2400Wh ÷ 600W = 4 hours. Actual runtime may drop 20–30% due to inefficiencies like temperature and aging.
What parameters affect 200Ah battery runtime?
Key factors include load current, battery voltage, and discharge depth. A 48V 200Ah lithium battery stores 9.6kWh—double the energy of 24V systems. Pro Tip: Lithium batteries maintain voltage better under load than lead-acid, delivering more usable capacity.
How to calculate for AC appliances?
Add inverter efficiency (85–95%) to calculations: Runtime = (Battery Wh × Inverter Efficiency) ÷ Appliance Watts. A 2000W AC load with 12V 200Ah battery and 90% inverter efficiency: (2400Wh × 0.9) ÷ 2000W = 1.08 hours. Use pure sine wave inverters for motor-driven appliances to avoid 10–15% efficiency loss.
| Appliance Type | Efficiency Adjustment |
|---|---|
| Resistive (heaters) | +5% runtime |
| Inductive (motors) | -15% runtime |
Does temperature impact calculations?
Absolutely. At -20°C, lead-acid batteries lose 50% capacity, while lithium-ion drops 25%. Always derate calculations for cold environments: Adjusted Capacity = Rated × (1 – Temp Derating%). For example, 200Ah at -20°C becomes 100Ah (lead-acid) or 150Ah (LiFePO4).
How do parallel vs series configurations affect runtime?
Parallel connections increase capacity (Ah) while maintaining voltage. Two 12V 200Ah batteries in parallel = 12V 400Ah (9600Wh). Series connections increase voltage while keeping capacity: Two 12V 200Ah in series = 24V 200Ah (9600Wh). Runtime remains identical if total energy (Wh) matches load requirements.
| Configuration | Voltage | Capacity |
|---|---|---|
| Single Battery | 12V | 200Ah |
| Parallel (2x) | 12V | 400Ah |
| Series (2x) | 24V | 200Ah |
What’s the practical difference between lead-acid and lithium?
Lead-acid provides only 50% usable capacity (100Ah for 200Ah battery) versus lithium’s 80% (160Ah). A 200Ah LiFePO4 at 12V gives 1536Wh (160Ah × 9.6V average) versus lead-acid’s 600Wh (100Ah × 12V × 50% DoD).
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Redway Battery Expert Insight
FAQs
Never combine batteries with >6 months age difference—capacity mismatch causes premature failure.
How long will 200Ah run a 100W fridge?
At 12V: (200Ah × 12V × 0.8 efficiency) ÷ 100W = ~19.2 hours for lithium. Lead-acid: ~10 hours (50% usable).
What size solar panel charges 200Ah daily?
Requires ~600W solar (200Ah × 12V ÷ 4 sun hours × 1.25 losses). Lithium charges faster—2C rate allows full charge in 1.5 hours.
How Long Will a 120Ah Battery Run a 12V Fridge?
