Battery planning

Battery Runtime Calculator

Estimate how long your 12V, 24V, or 48V battery bank will power connected appliances in hours and minutes, factoring in DOD reserves, battery health, and inverter losses.

Calculate estimated runtime

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Estimated runtime

7 h 12 min

≈ 7.2 hours

A planning estimate based on your battery energy and average device load.

Model Standard:IEEE 485•Peukert Physics•IEC 60896

Usable Energy Window80% Usable

Reserve 20%

0.80 kWh

Usable (80%)

Reserve (20%)

⏱️ Outage Survival Clock & Timeline7h 12m Backup

Usable Power (80%)

20% Reserve

100% Full

50% Half-Life

20% Low Cutoff

📈 Estimated Runtime vs. Continuous Load12V • 83.33333333333333Ah • 80% DoD

Battery capacity: 1,000 Wh
Usable battery energy: 800 Wh
Device load: 100 W average
Battery-side load: 111 W

Energy Conversion Flow

Nominal Capacity1,000 Wh

Rated pack capacity

Usable After Reserve800 Wh

80% usable DOD window

Effective Delivered Energy720 Wh

After 90% efficiency

Runtime at different loads

75 W: 9 h 36 min
100 W Your load: 7 h 12 min
125 W: 5 h 46 min

Assumptions used

Battery type: LiFePO4 / LFP
Starting charge: 100%
Reserve: 20%
Battery health: 100%
AC inverter efficiency: 90%

If your actual load is 10% higher, runtime is about 9% shorter.

Want a more accurate result?

Use your battery's actual Wh/Ah rating, your appliance's measured or nameplate watts, inverter efficiency if known, current charge, and battery health.

📊 Battery Backup Runtime Quick Lookup Matrix (12V LiFePO4 / 90% DoD)

Estimated runtimes across standard battery capacities under continuous AC appliance loads (92% inverter efficiency).

Continuous AC Load	50 Ah (640 Wh)	100 Ah (1.28 kWh)	200 Ah (2.56 kWh)	300 Ah (3.84 kWh)
50 W (Wi-Fi, LED lights, CPAP)	10.6 hrs	21.2 hrs	42.4 hrs	63.6 hrs
100 W (Laptop + Fridge cycle)Popular	5.3 hrs	10.6 hrs	21.2 hrs	31.8 hrs
250 W (Desktop PC + Monitor)	2.1 hrs	4.2 hrs	8.5 hrs	12.7 hrs
500 W (Sump pump / Refrigerator)	1.1 hrs	2.1 hrs	4.2 hrs	6.4 hrs
1,000 W (Microwave / Power tools)	0.5 hrs	1.1 hrs	2.1 hrs	3.2 hrs
1,500 W (Space heater / Kettle)	0.3 hrs	0.7 hrs	1.4 hrs	2.1 hrs

Assumes 12.8V nominal LiFePO4 chemistry with 90% DoD and 25W inverter tare dissipation.Source: IEEE Std 485 / Peukert Equation (k = 1.02)

Engineering WalkthroughGoverned by IEEE Std 485 / Peukert (1897)

How to Calculate Battery Backup Runtime (Step-by-Step)

How to calculate battery discharge duration step-by-step using Peukert's law, depth of discharge windows, and power conversion efficiencies.

Calculate Effective Battery-Side Load Current

Divide the AC load wattage by nominal battery voltage and inverter efficiency to find the total DC Amperes drawn from the battery bank.

I = \frac{P_{\text{load}}}{V_{\text{nominal}} \times \eta_{\text{inverter}}}

💡 Standard Example: 100W load at 12V with 92% inverter efficiency draws: 100 / (12 × 0.92) = 9.06 Amps DC

Determine Usable Amp-Hour Capacity

Multiply rated manufacturer Amp-hour capacity by maximum safe Depth of Discharge (0.80–0.90 for LiFePO4; 0.50 for Lead-Acid) and battery state of health.

C_{\text{usable}} = C_{\text{rated}} \times \text{DoD}_{\text{max}} \times \text{Health}

💡 Standard Example: 100Ah LiFePO4 battery at 90% DoD and 100% Health provides: 100 × 0.90 × 1.0 = 90 Usable Ah

Solve for Runtime Duration via Peukert Equation

Apply Peukert's Law to account for high-current capacity degradation under heavier loads.

t = H \cdot \left( \frac{C_{\text{usable}}}{I \cdot H} \right)^k

💡 Standard Example: 90 usable Ah / 9.06A continuous current = ~9.9 hours of continuous runtime

How to Calculate Battery Backup Runtime

Enter Battery Capacity (Ah or Wh): Choose nominal system voltage (12V, 24V, 48V) and Amp-hour capacity.
Select or Enter Appliance Load (Watts): Enter continuous average running watts or use the appliance load builder.
Set Depth of Discharge (DOD) Reserve: Lithium LiFePO4 batteries allow 80% to 90% usable capacity; Lead-Acid/AGM allows 50%.
Review Operating Duration: View exact hours and minutes of backup power available.

⚡

Battery Discharge & Backup Flow Topology

Multi-source charging, chemical storage management, and pure sine wave inverted backup delivery.

🔌InputGrid / Solar InputPrimary Energy Input

⚡ProtectionSmart BMS ChargerMulti-Stage CC/CV Charging

🔋ReservesBattery Bank12V / 24V / 48V Storage

🔄InverterPure Sine InverterDC to 120V/240V AC (88–92%)

💡ProtectedCritical SubpanelRefrigeration, Medical, Wi-Fi

Engineering Principle: Continuous AC backup runtime is determined by usable Depth of Discharge (DOD) and inverter conversion efficiency.

Common Battery Runtime Scenarios (100Ah vs 200Ah LiFePO4)

Estimated continuous operating hours for popular appliances powered by a 12V lithium battery (80% usable capacity, 90% inverter efficiency):

Estimated runtime on 12V 100Ah (960Wh usable) vs 12V 200Ah (1,920Wh usable)
Device / Load	Average Power	100Ah 12V Runtime	200Ah 12V Runtime
Wi-Fi Router + Modem	15 W	~57.6 hours (2.4 days)	~115.2 hours (4.8 days)
CPAP Machine (no heated humidifier)	35 W	~24.7 hours (~3 nights)	~49.4 hours (~6 nights)
Starlink Satellite Terminal	50 W	~17.3 hours	~34.6 hours
12V Portable Camping Fridge	30 W avg (cycling)	~28.8 hours (1.2 days)	~57.6 hours (2.4 days)
Desktop PC + Monitor	200 W	~4.3 hours	~8.6 hours
Full-Size Refrigerator (cycling)	150 W avg	~6.3 hours	~12.7 hours

Battery Runtime Calculation Formula

Calculates exact continuous running duration by determining net usable stored energy after Depth-of-Discharge (DOD) limits, battery health degradation, and inverter conversion losses.

01Runtime (hours) = (Capacity_Wh × Usable_SOC × Battery_Health × Efficiency) / Load_Watts

Variable Definitions

Capacity_WhNominal Battery Energy(Wh): Rated battery watt-hours (or Volts × Amp-Hours).
Usable_SOCUsable State of Charge Window(fraction): Fraction of capacity available above minimum reserve (e.g., 80% for LiFePO4, 50% for Lead-Acid).
Battery_HealthState of Health (SOH)(fraction): Available capacity relative to original factory rating (default 100%).
EfficiencyConversion Efficiency (η)(fraction): Inverter efficiency for AC loads (85%–93%) or DC-DC step efficiency.
Load_WattsContinuous Power Demand(W): Average real-time appliance consumption (Running Watts × Duty Cycle).

Engineering Notes & Standards

For intermittent loads like refrigerators and AC compressors, average load = running watts × duty cycle (typically 30%–45%).
Lead-acid and AGM batteries experience Peukert capacity loss under heavy discharge rates (>0.2C).

Frequently Asked Questions (FAQ)

How long will a 100Ah 12V battery run a refrigerator?

A standard household refrigerator averaging 150W (cycling with a ~35% compressor duty cycle) will run for approximately 6.3 hours on a 12V 100Ah LiFePO4 battery (assuming 80% usable capacity and 90% inverter efficiency). On a 200Ah battery, it will run for about 12.7 hours.

How long will a 100Ah battery run a CPAP machine?

A CPAP machine consuming 35W without a heated humidifier will run for approximately 24.7 hours on a 12V 100Ah LiFePO4 battery, or around 3 full 8-hour nights of sleep before needing recharge.

Why does a 12V 100Ah battery not provide the full 1,200 watt-hours?

Nominal energy is 12V × 100Ah = 1,200Wh. However, usable capacity is reduced by minimum state-of-charge reserve limits (typically 20% for LiFePO4 or 50% for Lead-Acid) and AC inverter conversion losses (typically 85%–92% efficiency).

How do I calculate battery runtime for AC appliances?

Divide usable battery watt-hours by the battery-side load. For AC equipment: Usable Wh = Rated Wh × Usable Fraction. Battery-Side Load = Appliance Watts ÷ Inverter Efficiency. Runtime Hours = Usable Wh ÷ Battery-Side Load.