--- title: "Battery Backup Time Calculator for Inverters (Ah to Hours)" description: "Calculate inverter battery backup time for home use. Enter battery Ah, number of batteries and the fans, lights and TV you run to get hours of backup." canonical: https://batteryruntimecalculator.com/inverter-battery-backup-calculator language: en updated: 2026-11-10 source_revision: 59f9d32 maintainer: Battery Runtime Calculator (hello@batteryruntimecalculator.com) --- # Inverter Battery Backup Time Calculator Find out how many hours your home inverter will run fans, lights and a TV during a power cut. Updated November 10, 2026 Quick answer A 12 V 150 Ah tubular battery runs a 250 W load (two fans, four LED lights, a TV and a router) for about **3 h 52 min**. A 200 Ah battery stretches that to about **5 h 33 min**. Estimated runtime 3 h 52 min ≈ 3.87 hours on 1,800 Wh at 250 W Usable energy 1,530 Wh Battery current 24.5 A Power from battery 294 W Discharge rate 0.16C - Draining lead-acid past 50% shortens its life. 85% is fine for occasional outages but not for daily cycling. How this was worked out 1. Battery energy: 1,800 Wh rated 2. Power drawn from the battery: 250 W ÷ 85% efficiency = 294 W 3. Rate effect (Peukert 1.25): the battery delivers 74% of its rating at this load 4. Runtime: 1,800 Wh × 74% × 85% usable ÷ 294 W = 3.87 h Runtime at other loads | Load | Runtime | | --- | --- | | 63 W | 20 h 39 min | | 125 W | 9 h 12 min | | 250 W | 3 h 52 min | | 375 W | 2 h 20 min | | 500 W | 1 h 38 min | ## Inverter battery backup time chart Backup time for one 12 V tubular battery at common household loads, with 85% inverter efficiency and the inverter cutting off at about 85% discharge. For a 24 V inverter with two batteries, roughly double the time. | Load | 100 Ah | 150 Ah | 200 Ah | 220 Ah | | --- | --- | --- | --- | --- | | 100 W | 7 h 20 min | 12 h 10 min | 17 h 20 min | 19 h 4 min | | 200 W | 3 h 5 min | 5 h 7 min | 7 h 20 min | 8 h 15 min | | 300 W | 1 h 51 min | 3 h 5 min | 4 h 25 min | 4 h 58 min | | 500 W | 59 min | 1 h 38 min | 2 h 20 min | 2 h 38 min | | 800 W | 33 min | 54 min | 1 h 18 min | 1 h 28 min | ## 150Ah battery backup time A 150 Ah tubular battery is the most common size for home inverters. One battery on a 12 V inverter stores 1.8 kWh; two on a 24 V inverter store 3.6 kWh. At 500 W, one 150 Ah battery gives about 1 h 38 min of backup, and two give about 3 h 52 min. | Load | 1 × 150 Ah (12 V) | 2 × 150 Ah (24 V) | | --- | --- | --- | | 100 W | 12 h 10 min | 26 h 1 min | | 200 W | 5 h 7 min | 12 h 10 min | | 300 W | 3 h 5 min | 7 h 20 min | | 400 W | 2 h 9 min | 5 h 7 min | | 500 W | 1 h 38 min | 3 h 52 min | | 600 W | 1 h 18 min | 3 h 5 min | | 800 W | 54 min | 2 h 9 min | | 1000 W | 41 min | 1 h 38 min | ## 200Ah battery backup time A 200 Ah battery stores a third more energy than a 150 Ah one, but at 500 W its backup is about 43% longer, because a bigger battery is drained more gently and loses less to Peukert’s law. At 500 W, one 200 Ah battery gives about 2 h 20 min, and two on a 24 V inverter about 5 h 33 min. | Load | 1 × 200 Ah (12 V) | 2 × 200 Ah (24 V) | | --- | --- | --- | | 100 W | 17 h 20 min | 34 h 41 min | | 200 W | 7 h 20 min | 17 h 20 min | | 300 W | 4 h 25 min | 10 h 30 min | | 400 W | 3 h 5 min | 7 h 20 min | | 500 W | 2 h 20 min | 5 h 33 min | | 600 W | 1 h 51 min | 4 h 25 min | | 800 W | 1 h 18 min | 3 h 5 min | | 1000 W | 59 min | 2 h 20 min | ## Battery backup time formula ``` Backup (h) = Ah × V × number of batteries × efficiency ÷ load (W) ``` This is the formula most battery shops use, often with a single 0.8 factor for efficiency. For 150 Ah and 250 W it gives 5.8 hours. The calculator above goes two steps further: - **Inverter cut-off.** The inverter switches off when the battery voltage falls to around 10.5 V, before the battery is completely empty, so we count about 85% of its capacity. - **Peukert’s law.** Lead-acid batteries are rated over 20 hours. Drained in 4 or 5 hours they deliver noticeably less, so backup at higher loads is shorter than the simple formula suggests. Both effects together explain why the calculator shows 3 h 52 min instead of 5.8 hours. If your battery is a few years old, lower battery health in Advanced settings as well. The details are in [how battery runtime is calculated](https://batteryruntimecalculator.com/how-battery-runtime-is-calculated). ## Typical power use of home appliances | Appliance | Typical watts | | --- | --- | | Ceiling fan (standard) | 70–80 W | | Ceiling fan (BLDC) | 28–35 W | | LED bulb | 7–12 W | | LED tube light | 18–22 W | | LED TV (32–43 inch) | 40–80 W | | Wi-Fi router | 6–12 W | | Laptop charging | 45–90 W | | Refrigerator (average over a day) | 40–80 W | | Desktop computer with monitor | 150–250 W | Check the rating label for your own appliances. Air conditioners, geysers, irons and microwaves draw 1,000–2,000 W and are not suitable for a typical home inverter. ## Tips to get longer backup - Switch to BLDC fans and LED lights: they cut the load by more than half. - Keep tubular battery water topped up with distilled water and the terminals clean. - Make sure the battery reaches full charge between power cuts; a battery that never fully charges loses capacity. - For daily long cuts, size the battery properly with the [battery size calculator](https://batteryruntimecalculator.com/battery-size-calculator), or add [solar charging](https://batteryruntimecalculator.com/solar-battery-calculator). ## Frequently asked questions ### How do you calculate inverter battery backup time? Backup time (hours) = battery Ah × battery voltage × number of batteries × efficiency ÷ load in watts. For a 150 Ah 12 V battery and a 250 W load, a common rule of thumb with 80% overall efficiency gives 150 × 12 × 0.8 ÷ 250 = 5.8 hours. Real tubular batteries deliver less at higher loads, which this calculator accounts for, so it usually shows a lower and more realistic figure. ### How long will a 150Ah inverter battery last? With a 250 W load (two ceiling fans, a few LED lights, a TV and a router), a single 12 V 150 Ah tubular battery gives about 3 h 52 min of backup. At 100 W it lasts about 12 h 10 min. ### How long will a 200Ah battery last on an inverter? A 12 V 200 Ah tubular battery runs a 300 W load for about 4 h 25 min and a 500 W load for about 2 h 20 min. Two 200 Ah batteries on a 24 V inverter roughly double those times. ### Do two batteries double the backup time? Yes, for the same load. A 24 V inverter uses two 12 V batteries in series, which stores twice the energy of one battery of the same Ah, so backup roughly doubles. Set the number of batteries to 2 in the calculator. ### Which battery is best for inverter backup: tubular or lithium? Tall tubular lead-acid batteries are the most common and cheapest per Ah, but need water top-ups and give less at high loads. Lithium (LiFePO4) inverter batteries cost more, need no maintenance, charge faster and deliver close to their full rating, so a 100 Ah lithium battery often matches a 150 Ah tubular one in real backup. ### How many watts does a ceiling fan use? A standard ceiling fan uses about 70–80 W at full speed, and an energy-efficient BLDC fan about 28–35 W. Running fans at lower speed reduces the load and stretches backup time. ## More battery calculators - [Battery runtimeRuntime for any battery and load, in Ah or Wh, AC or DC.](https://batteryruntimecalculator.com/) - [Battery life (mAh)mAh and mA to hours, with sleep current and duty cycle.](https://batteryruntimecalculator.com/battery-life-calculator) - [Battery sizeHours you need in, battery Ah, Wh and count out.](https://batteryruntimecalculator.com/battery-size-calculator) - [Solar battery bankDaily kWh and days of autonomy to a battery bank size.](https://batteryruntimecalculator.com/solar-battery-calculator) - [UPS runtimeBackup minutes for a computer, router or NAS on a UPS.](https://batteryruntimecalculator.com/ups-runtime-calculator) - [Power station runtimeWh rating to runtime for portable power stations.](https://batteryruntimecalculator.com/power-station-runtime-calculator) - [12V battery runtime12V deep-cycle runtime for RVs, vans and boats.](https://batteryruntimecalculator.com/12v-battery-runtime-calculator) - [Ah to Wh converterAmp hours, watt hours and kWh at any voltage.](https://batteryruntimecalculator.com/ah-to-wh-calculator) - [mAh to Wh convertermAh to Wh for power banks, with the 100 Wh flight limit.](https://batteryruntimecalculator.com/mah-to-wh-calculator) - [Charge timeHours to charge from any state of charge, by charger amps.](https://batteryruntimecalculator.com/battery-charge-time-calculator) - [How runtime is calculatedThe formulas behind every calculator, with worked examples.](https://batteryruntimecalculator.com/how-battery-runtime-is-calculated)