{
    "name": "Battery Backup Runtime Calculator",
    "url": "https://calculators.geekmidst.com/calculators/battery-backup-runtime-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/battery-backup-runtime-calculator.md",
    "category": "Energy & environment",
    "description": "Estimate how long a battery, UPS or inverter backup will run a load from its Ah and voltage or kWh, usable depth of discharge and inverter efficiency.",
    "summary": "Runtime is the battery’s usable energy divided by the power the load draws. Usable energy is the rated capacity times the depth of discharge you allow, less inverter losses.",
    "also_called": [
        "UPS runtime calculator",
        "Inverter backup time calculator",
        "Battery life calculator"
    ],
    "applies_to": "Worldwide",
    "last_updated": "2026-10-29",
    "computation": "Results are computed in the visitor’s browser on the HTML page. This API describes the calculator; it does not compute results.",
    "inputs": [
        {
            "name": "capacity",
            "label": "Battery capacity",
            "type": "number",
            "default": "200"
        },
        {
            "name": "capacity_unit",
            "label": "Capacity in",
            "type": "segmented",
            "default": "ah",
            "options": {
                "ah": "Amp-hours",
                "kwh": "kWh"
            }
        },
        {
            "name": "voltage",
            "label": "Battery bank voltage",
            "type": "number",
            "default": "12",
            "unit": "V"
        },
        {
            "name": "dod",
            "label": "Usable depth of discharge",
            "type": "number",
            "default": "50",
            "unit": "%"
        },
        {
            "name": "efficiency",
            "label": "Inverter efficiency",
            "type": "number",
            "default": "90",
            "unit": "%"
        },
        {
            "name": "load",
            "label": "Load",
            "type": "number",
            "default": "300",
            "unit": "W"
        }
    ],
    "outputs": [
        {
            "key": "runtime_text",
            "label": "Backup time",
            "format": "text"
        },
        {
            "key": "runtime_hours",
            "label": "Backup time in hours",
            "format": "number"
        },
        {
            "key": "total_wh",
            "label": "Rated energy",
            "format": "number"
        },
        {
            "key": "usable_wh",
            "label": "Usable energy delivered",
            "format": "number"
        },
        {
            "key": "battery_current",
            "label": "Current drawn from the battery",
            "format": "number"
        }
    ],
    "formula": {
        "text": "Wh = Ah × V (or kWh × 1000);  Runtime (h) = Wh × DoD × Inverter efficiency ÷ Load (W);  Battery current = Load ÷ Efficiency ÷ V",
        "variables": {
            "Ah": "rated amp-hour capacity",
            "V": "battery bank voltage",
            "DoD": "share of capacity you allow to be used",
            "Load": "power drawn by the connected devices"
        }
    },
    "worked_example": {
        "inputs": {
            "capacity": "200",
            "capacity_unit": "ah",
            "voltage": "12",
            "dod": "50",
            "efficiency": "90",
            "load": "300"
        },
        "steps": [
            "Rated energy = 200 Ah × 12 V = 2,400 Wh.",
            "Usable = 2,400 × 0.50 × 0.90 = 1,080 Wh.",
            "Runtime = 1,080 ÷ 300 W = 3.6 h = 3 h 36 min."
        ],
        "result": "A 12 V 200 Ah battery used to 50% through a 90%-efficient inverter runs a 300 W load for about 3 hours 36 minutes."
    },
    "interpretation": "Treat the result as a best case. At high currents, in the cold, or with an older battery, real runtime is shorter, so allow a margin for anything critical.",
    "assumptions": [
        "The load is constant for the whole runtime.",
        "The battery delivers its rated capacity at this discharge rate."
    ],
    "limitations": [
        "Ignores the Peukert effect (lead-acid capacity drops at high currents), temperature and battery age.",
        "Inverter standby consumption is not included."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "Why not use 100% of the battery?",
            "answer": "Deep discharges shorten battery life, especially for lead-acid. Most systems cut off before the battery is fully empty."
        },
        {
            "question": "How do I find my load in watts?",
            "answer": "Add up the rated watts of the devices on backup, or read the output power from the inverter display."
        }
    ],
    "sources": [],
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    "disclaimer": null,
    "publisher": "GM¹X CalcVerse"
}