LetUsCalc
Free UPS Backup Time Tool

Battery Runtime Calculator

Use our free battery runtime calculator to estimate backup hours for APC UPS, CyberPower, and standalone battery banks. This UPS battery runtime calculator supports 12V lead-acid, LiFePO4 lithium, and custom loads in watts — instant results with no sign-up required.

Battery Runtime Calculator

UPS · APC · CyberPower

Battery Specifications

Load & Battery Type

Sum of all devices connected to the battery or UPS

DoD multiplier: 0.5 (50% usable)

Formula: Runtime = (Ah × V × DoD) ÷ Watts

Backup Runtime Results

Enter battery capacity, voltage, and load to estimate runtime

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What Is a Battery Runtime Calculator?

A battery runtime calculator estimates how long your battery or UPS system will power connected devices before depletion. Whether you need an APC UPS runtime calculator, a CyberPower runtime calculator, or a general UPS run time calculator — the math is the same: convert amp-hours and voltage to watt-hours, apply depth of discharge, then divide by your total load in watts.

Our tool works as an APC runtime calculator, CyberPower UPS runtime calculator, and lithium battery run time calculator in one interface. Enter your specs and get backup time in hours and minutes instantly.

How to Calculate Battery Runtime Manually

Follow these steps to manually calculate backup time using the Capacity × Voltage × DoD formula — the same logic behind every battery runtime calculator watts tool:

  1. 1
    Calculate Total Watt-Hours

    Total Wh = Capacity (Ah) × Voltage (V). Example: 100 Ah × 12V = 1,200 Wh.

  2. 2
    Apply Depth of Discharge

    Usable Wh = Total Wh × DoD. Lead-acid: × 0.50. LiFePO4: × 0.90. Lithium-ion: × 0.80.

  3. 3
    Divide by Power Load

    Runtime (hours) = Usable Wh ÷ Load (W). Example: 600 Wh ÷ 200W = 3 hours.

Master Formula

Runtime (hrs) = (Ah × V × DoD) ÷ Watts

12V Lead-Acid vs. LiFePO4 Runtime Comparison

A standard 12v battery run time calculator using lead-acid chemistry applies only 50% depth of discharge — draining further damages the battery. An advanced lifepo4 battery run time calculator unlocks 90% DoD, delivering dramatically longer backup from identical Ah and voltage ratings.

Battery TypeDoD100Ah × 12V Usable WhRuntime @ 200W
Lead-Acid / AGM (50% DoD)50%600 Wh3 Hours 0 Minutes
LiFePO4 / Lithium Iron Phosphate (90% DoD)90%1080 Wh5 Hours 24 Minutes
Custom Lithium-Ion (80% DoD)80%960 Wh4 Hours 48 Minutes

Key takeaway: A 100Ah LiFePO4 12V battery delivers 1,080 Wh usable vs. only 600 Wh from lead-acid — nearly 80% more runtime at the same load. This is why lithium UPS upgrades are popular for home labs and network closets.

Common Device Backup Duration Reference

Estimated backup times using a 100Ah × 12V LiFePO4 battery (90% DoD = 1,080 Wh usable) — compare how load watts dramatically affect your UPS battery runtime calculator output:

Device / LoadPower DrawEst. Runtime (100Ah LiFePO4)Notes
WiFi Router15 W72 Hours 0 MinutesTypical home mesh or cable modem router
Laptop Charger65 W16 Hours 36 MinutesSingle laptop on AC adapter
Refrigerator (Mini)150 W7 Hours 12 MinutesCompact fridge — surge higher on compressor start
Desktop PC200 W5 Hours 24 MinutesOffice workstation, no dedicated GPU
Gaming PC400 W2 Hours 42 MinutesHigh-end GPU + CPU under load
Window AC Unit900 W1 Hour 12 MinutesSmall room air conditioner — high surge on startup

A WiFi Router at 15W runs ~72 hours on this bank, while a Gaming PC at 400W lasts only ~2.7 hours — illustrating why accurate wattage input is critical for any battery runtime calculator.

Battery Runtime Calculation Example

Sample: APC-Style 12V 100Ah AGM Battery, 200W Load

  • • Capacity: 100 Ah
  • • Voltage: 12V
  • • Battery: Lead-Acid / AGM (50% DoD)
  • • Load: 200 Watts
Total Wh = 100 × 12 = 1,200 Wh
Usable Wh = 1,200 × 0.50 = 600 Wh

Result: 3 Hours 0 Minutes

600 Wh ÷ 200W = 3.0 hours of backup runtime

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