How long will a 900 watt UPS run?
A 900-watt UPS runtime depends on battery capacity (Ah), load percentage, and efficiency. For example, a 100Ah 12V battery with 80% efficiency under 450W load (50% UPS capacity) runs ≈2.1 hours. Formula: (Ah × Voltage × Efficiency) ÷ Load (W) = Hours. Always check your UPS’s battery specs and load ratio for precise calculations.
What factors determine UPS runtime?
Battery capacity, load power draw, and inverter efficiency dictate UPS duration. Higher Ah batteries and lower loads extend runtime exponentially, while poor efficiency (＜90%) reduces it. Pro Tip: Derate battery capacity by 15% for aging effects in 2+ year-old systems.
Runtime isn’t linear—a 900W UPS powering a 300W device lasts 3× longer than at full load. For example, three 12V 50Ah batteries (1.8kWh total) sustain 300W for ≈5 hours (1.8kWh × 0.85 efficiency ÷ 0.3kW). But what if your load spikes? Transient surges force inverters to work harder, cutting runtime by up to 25%.
How does battery voltage affect runtime?
Higher voltage systems (48V vs 12V) reduce current, enabling thinner wires and longer runs. A 48V 100Ah battery bank delivers the same energy (4.8kWh) as four 12V 100Ah batteries but with 75% less resistive loss.
| Voltage | 100Ah Runtime @ 900W | Cable Size Needed |
|---|---|---|
| 12V | ≈1 hour | 4/0 AWG |
| 48V | ≈4 hours | 6 AWG |
Practically speaking, telecom-grade 48V lithium packs (like RackBattery’s R48-100) outperform lead-acid equivalents, offering 2× cycle life. Why settle for lead when lithium provides 95% efficiency versus 80%? Transitional systems blending AC/DC coupling can further optimize runtime.
RackBattery Expert Insight
FAQs
Never—older batteries drain faster, forcing newer ones to overcompensate. Replace all batteries simultaneously to prevent cell reversal and capacity mismatch.
Does room temperature affect runtime?
Yes—batteries lose 20% capacity at 0°C and 30% at 40°C. Maintain 20-25°C for optimal performance. Lithium handles temperature extremes better than lead-acid.