⚡ Energy Management Dashboard

Inverter Battery Runtime Calculator

Q: How do I calculate inverter battery backup time?

Use: Runtime = (Ah × V × DoD × SoC × efficiency) ÷ load (W). This gives hours. Multiply the decimal by 60 for minutes.

Q: What is the difference between Ah and Wh?

Ah measures charge capacity; Wh measures energy. Wh = Ah × voltage. A 100 Ah, 12 V battery holds 1,200 Wh nominal energy.

Q: Why is usable capacity lower than nominal?

Depth of discharge limits how much you can safely draw. Lead-acid: ~50%; LiFePO₄: ~80%. Inverter efficiency also reduces usable energy.

Q: Does inverter efficiency really matter?

Yes. A 80% efficient inverter wastes 20% of battery energy as heat. Premium inverters reach 90–95%, giving noticeably longer runtime.

Q: Can I run multiple appliances at once?

Yes — sum their wattages. But check surge watts for motor-driven appliances and ensure your inverter can handle the total plus surge.

Q: How does temperature affect runtime?

Cold reduces available capacity. Lead-acid loses ~1% per °C below 25°C. LiFePO₄ is more tolerant but still benefits from moderate temperatures.

Q: What is power factor and why does it matter?

Power factor (PF) is real power ÷ apparent power. Loads with PF < 1 draw more current for the same wattage, so inverter VA rating must be higher.

Q: Why does my actual runtime fall short of the estimate?

Battery age, temperature, Peukert effect, inverter idle draw, and surge loads all reduce real-world runtime. Use our estimate as an optimistic baseline, then derate by 10–20% for planning.

See exactly how long your inverter will run your appliances. Enter battery capacity, load, and efficiency — get a real-world backup time estimate with a live energy-flow dashboard.

Battery Bank

Source

Battery Voltage per battery

Capacity per battery (Ah) 100 Ah

20400

Number of batteries 1

112

Battery type (sets typical DoD)

Load

Appliances

Quick add appliance

Total load (W) 300 W

10 W5,000 W

Inverter efficiency

Power factor

State & Limits

Real-world

State of charge (SoC) 100%

Depth of discharge (DoD) 50%

10%90%

Energy Flow

75%

Battery Bank

1 × 12 V · 100 Ah

INVERTER 85% eff

Inverter

300 W

Appliances

Total capacity

100 Ah

@ 12 V

Energy

1,200 Wh

nominal

Usable energy

510 Wh

after DoD

Total load

300 W

continuous

Estimated inverter runtime

1h 42m

at 85% efficiency · 300 W load

🔋 Remaining: 510 Wh ⏱️ 1.70 h

💡 How this is calculated

Usable energy = capacity × voltage × DoD × SoC. Runtime = usable energy × inverter efficiency ÷ load. Actual results vary with temperature, battery age, and load profile.

Quick answer

Formula: Runtime (h) = (Battery Ah × Voltage × DoD × SoC × Inverter efficiency) ÷ Load (W).

Example: 12 V, 100 Ah lead-acid at 50% DoD, 85% inverter efficiency, 300 W load → ~1 h 42 min.

Key idea: Ah is charge; Wh is energy. Usable energy is always less than nominal.

Lead-acid: keep DoD ≤ 50% for longevity.
LiFePO₄: can safely use 80–90% DoD.
Higher load → shorter runtime, non-linearly.
Cold reduces capacity; heat accelerates aging.
Power factor < 1 increases apparent load (VA).

Ah vs Wh: the difference that matters

Ampere-hours (Ah) measures charge — how much current a battery can deliver over time. Watt-hours (Wh) measures energy — the actual work available. Voltage connects them:

Wh = Ah × V

A 100 Ah battery at 12 V stores 1,200 Wh nominally. But you cannot use all of it. Depth of discharge (DoD) and inverter efficiency cut usable energy significantly.

Battery type cheat sheet

Type	Typical DoD	Cycle life
Flooded lead-acid	50%	300–500
AGM / Gel	60%	500–800
LiFePO₄	80–90%	2,000–5,000

Cycle life depends on temperature, charge rate, and depth of discharge.

Why real runtime differs from theory

🌡️

Temperature

Capacity drops ~1% per °C below 25°C for lead-acid. LiFePO₄ is more stable but still affected.

📉

Battery aging

Internal resistance rises with age, reducing usable capacity and efficiency.

⚡

Load profile

Peukert effect: high discharge currents reduce effective Ah. Surge loads matter too.

🔌

Inverter overhead

Idle draw and conversion losses can consume 5–20% of energy even at low load.

Typical appliance loads

Appliance	Running watts	Surge watts	Notes
LED bulb (10 W)	10 W	—	Resistive, PF ≈ 1
Ceiling fan	70–90 W	~120 W	Motor, PF ≈ 0.8
Laptop + monitor	80–150 W	—	SMPS, PF ≈ 0.9
Refrigerator (1 door)	100–200 W	600–800 W	Compressor surge
Microwave	800–1200 W	—	High draw, short duty
Water pump (0.5 HP)	375 W	1100+ W	High surge, PF ≈ 0.7

Always size your inverter for surge watts, not just running watts.

Frequently asked questions

How do I calculate inverter battery backup time? ▼

Use: Runtime = (Ah × V × DoD × SoC × efficiency) ÷ load (W). This gives hours. Multiply the decimal by 60 for minutes. Our calculator does this live as you adjust sliders.

What is the difference between Ah and Wh? ▼

Ah measures charge capacity; Wh measures energy. Wh = Ah × voltage. A 100 Ah, 12 V battery holds 1,200 Wh nominal energy.

Why is usable capacity lower than nominal? ▼

Depth of discharge limits how much you can safely draw. Lead-acid: ~50%; LiFePO₄: ~80%. Inverter efficiency also reduces usable energy.

Does inverter efficiency really matter? ▼

Yes. A 80% efficient inverter wastes 20% of battery energy as heat. Premium inverters reach 90–95%, giving noticeably longer runtime.

Can I run multiple appliances at once? ▼

Yes — sum their wattages. But check surge watts for motor-driven appliances and ensure your inverter can handle the total plus surge.

How does temperature affect runtime? ▼

Cold reduces available capacity. Lead-acid loses ~1% per °C below 25°C. LiFePO₄ is more tolerant but still benefits from moderate temperatures.

What is power factor and why does it matter? ▼

Power factor (PF) is real power ÷ apparent power. Loads with PF < 1 draw more current for the same wattage, so inverter VA rating must be higher. Our calculator uses PF for accurate load sizing.

Why does my actual runtime fall short of the estimate? ▼

Battery age, temperature, Peukert effect, inverter idle draw, and surge loads all reduce real-world runtime. Use our estimate as an optimistic baseline, then derate by 10–20% for planning.