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Battery Runtime Calculator: How Long Will a Battery Last?
Find out how long a 12 V battery, a power bank or a portable power station will run your devices, and until what time. Then see how long it takes to charge from the wall, a car or solar panels where you live, or the size you need to get through a power cut.
What it calculates. How long it lasts: the usable energy in the battery divided by what your devices draw, as hours and the clock time it runs out. How long to charge: the energy to put back divided by the charging power from a wall charger, a car’s 12 V socket or solar panels. What size I need: the capacity a list of devices needs for a number of days, and which power stations cover it.
Usable share. All of a lithium iron phosphate (LiFePO4) battery (Battle Born data sheet); half of a lead-acid battery, Trojan’s recommendation for a long life, with 80% as the most it should ever give; and 85% of a power station’s rated capacity, Jackery’s planning factor for the loss in its inverter.
Heavy loads and cold. A lead-acid battery gives less than its 20-hour rating when it is worked hard (Peukert’s law, with exponents worked out from Trojan’s published 5-hour and 20-hour ratings) and about half its capacity at 0°F (Trojan). An inverter loses about 10% and draws about 6 W just being on (Victron Phoenix 12/500).
Charging. A charger is capped at what the battery accepts: 0.5C for LiFePO4, 13% to 20% of the 20-hour capacity for lead-acid, which then needs a slow top-up past 80%. Solar uses the peak sun hours for your state from NREL’s PVWatts, as a yearly average and in the worst month.
What it leaves out. Battery ageing, lithium capacity loss in the cold, and the exact draw of your own devices: device figures are typical, and the watts on a label or a plug-in meter are better.
More options: usable share, inverter, temperature
The answer updates as you type. Battery figures: Battle Born, Trojan and Victron data sheets; power stations: makers' specifications; sun hours: NREL PVWatts. Reads MasterBrain V3 live.
Pick a battery and enter what it powers
Results show how long it lasts and until what time, each device's share, the charge time from a wall, car or solar, the size you need, the audit trail and export.
Results are estimates. Real runtime depends on the battery's age and health, how hard and how evenly it is worked, its temperature, and what the devices actually draw, which is often less than their rated watts and sometimes more when a motor starts. Power station figures are the makers' specifications. Solar charging uses a typical year at one reference city per state; shade, panel angle and cloudy spells change it. Follow the battery maker's limits for discharge, charging current and temperature.
Most battery calculators divide amp-hours by amps and stop there. That answer is right for a lithium battery on a small load and wrong for almost everything else: a lead-acid battery should only be run halfway down, gives less under a heavy load and in the cold, and an inverter eats into all of them.
This calculator counts each of those, with the battery makers’ own figures, and also tells you how long the battery takes to charge again, from the wall, the car or the sun.
Runtime in hours = battery watt-hours × the share you can use ÷ the watts you draw. A 12 V 100 Ah lithium (LiFePO4) battery holds 1,200 Wh and runs a 60 W load for about 20 hours, or about 16.5 hours through a 120 V inverter. A 12 V 100 Ah AGM battery, used to 50%, runs the same load for about 10 hours.
How to calculate battery runtime
- Find the capacity in watt-hours. Wh = amp-hours × volts. A 12 V 100 Ah battery holds 1,200 Wh. For phones and power banks, Wh = mAh ÷ 1,000 × 3.7 V, so 10,000 mAh is 37 Wh.
- Take the share you can use. All of it for LiFePO4, half for lead-acid, 85% for a power station.
- Divide by the load in watts. If the load is in amps, multiply by the battery voltage first. Through an inverter, divide the load by 0.9 and add about 6 W for the inverter itself.
So a 12 V 100 Ah LiFePO4 battery running a 60 W load lasts 1,200 ÷ 60 = 20 hours. Through an inverter it draws 60 ÷ 0.9 + 6 = 72.7 W, and lasts about 16.5 hours. For a list of devices that each run a few hours a day, add up their watt-hours a day (watts × hours) and divide the usable energy by that to get days.
How long a 100 Ah battery lasts
A 12 V 100 Ah battery on a steady 12 V load, straight from the battery. The AGM column is shorter than half the lithium one at heavy loads because of Peukert’s law (see below).
| Load | Amps | LiFePO4 | AGM |
|---|---|---|---|
| 12 W | 1.0 A | 4.2 days | 2.1 days |
| 24 W | 2.0 A | 2.1 days | 25 h |
| 60 W | 5.0 A | 20 h | 10 h |
| 120 W | 10 A | 10 h | 4.3 h |
| 240 W | 20 A | 5.0 h | 1.8 h |
| 600 W | 50 A | 2.0 h | 36 min |
| 1,200 W | 100 A | 1.0 h | 16 min |
Lithium vs lead-acid: why the same amp-hours last differently
- Usable share. Battle Born rates its 100 Ah LiFePO4 battery for 100% depth of discharge. Trojan recommends discharging its deep-cycle lead-acid batteries 50% or less, and calls 80% the maximum safe discharge: going deeper costs cycles.
- Heavy loads. A lead-acid battery’s rated amp-hours are measured over 20 hours. Drain it faster and it gives fewer: Trojan’s 8D-AGM is rated 230 Ah at the 20-hour rate but 179 Ah at the 5-hour rate. At 50 A, a 100 Ah AGM battery lasts about 36 minutes to 50%, not an hour. Lithium batteries barely lose capacity this way.
- Cold. Trojan says its batteries deliver 50% of their capacity at 0°F and 100% at 80°F. Lithium batteries keep their capacity better, but most refuse to charge below freezing: 25°F for the Battle Born battery, 32°F for the five power stations here that publish a limit.
How long a power station lasts
Hours on one full charge at 85% of the rated capacity. The refrigerator figure is a typical US main fridge’s average draw over a day, not the watts on its label, because a fridge’s compressor switches on and off.
| Power station | Fridge | CPAP | 100 W |
|---|---|---|---|
| EcoFlow RIVER 3 Plus (286 Wh) | 3.5 h | 4.3 h | 2.4 h |
| Jackery Explorer 1000 v2 (1,070 Wh) | 13 h | 16 h | 9.1 h |
| Anker SOLIX C1000 (1,056 Wh) | 13 h | 16 h | 9.0 h |
| EcoFlow DELTA 3 Plus (1,024 Wh) | 12 h | 16 h | 8.7 h |
| BLUETTI AC180 (1,152 Wh) | 14 h | 17 h | 9.8 h |
| EcoFlow DELTA Pro 3 (4,096 Wh) | 2.1 days | 2.6 days | 35 h |
A power station also has a maximum output. If the devices running together, or a motor starting, need more, it shuts off: the calculator warns you when a list is over it. Our guide to the best portable power stations compares these six device by device.
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| Best for | Pick | Key spec | Amazon |
|---|---|---|---|
| Camping and travel | EcoFlow RIVER 3 Plus | 286 Wh | Check price |
| Outages and RVs | Jackery Explorer 1000 v2 | 1,070 Wh | Check price |
| Most output for the size | Anker SOLIX C1000 | 1,056 Wh | Check price |
| 1,800 W, 4,000 cycles | EcoFlow DELTA 3 Plus | 1,024 Wh | Check price |
| Largest 1 kWh-class battery | BLUETTI AC180 | 1,152 Wh | Check price |
| Whole-home backup | EcoFlow DELTA Pro 3 | 4,096 Wh | Check price |
- 286 Wh
- 600 W (1,200 W surge)
- 1,070 Wh
- 1,500 W (3,000 W surge)
- 1,056 Wh
- 1,800 W (2,400 W surge)
- 1,024 Wh
- 1,800 W
- 1,152 Wh
- 1,800 W (2,700 W peak)
- 4,096 Wh
- 4,000 W (6,000 W X-Boost)
How long to charge a battery
Charge time = the energy to put back ÷ the charging power. A bigger charger only helps up to what the battery accepts, and lead-acid charges at full speed only to about 80%, then needs a slow top-up.
| Charger | LiFePO4 | AGM | Flooded |
|---|---|---|---|
| 5 A | 16 h | 14 h | 16 h |
| 10 A | 8.1 h | 8.0 h | 10 h |
| 20 A | 4.0 h | 5.0 h | 8.6 h |
| 30 A | 2.7 h | 5.0 h | 8.6 h |
| 50 A | 1.6 h | 5.0 h | 8.6 h |
- Power stations charge at their own maximum AC input: 380 W for the RIVER 3 Plus, 1,500 W for the DELTA 3 Plus. From 20% that works out at about 36 and 33 minutes, though real charging slows near full.
- From a car, a 12 V socket gives about 100 W (BLUETTI’s figure), so a full 1,152 Wh AC180 takes over 11 hours of driving. The Jackery Explorer 1000 v2 takes 8 A from a car, about 96 W, so 20% to full takes about 9 hours of driving.
Charging from solar: sun hours by state
A solar panel makes about its rated watts × the peak sun hours × about 0.75 a day, the ratio between NREL’s PVWatts yield and the sunlight on the panel, which covers heat, wiring and conversion losses. Winter is the test: in Washington a 400 W panel set gives about 1,190 Wh on an average day but under 400 Wh in December.
| State | Yearly average | Lowest month |
|---|---|---|
| Arizona (Phoenix) | 6.54 | 4.75 (December) |
| California (Los Angeles) | 6.08 | 4.05 (December) |
| Florida (Jacksonville) | 5.48 | 3.90 (December) |
| Texas (Houston) | 5.22 | 3.50 (December) |
| Ohio (Columbus) | 4.60 | 2.33 (December) |
| New York (New York City) | 4.50 | 2.40 (December) |
| Washington (Seattle) | 3.95 | 1.32 (December) |
| Alaska (Anchorage) | 3.17 | 0.39 (December) |
Pick your state in the calculator for its own figures. A panel lying flat, shaded or facing the wrong way makes less, and a run of cloudy days less again. To size a rooftop system rather than a portable one, use the solar panel calculator.
What size battery do you need?
- Add up the watt-hours a day: each device’s watts × the hours it runs.
- If it runs through an inverter, divide by 0.9 and add 144 Wh a day for the inverter’s own draw.
- Multiply by the days it has to last, and divide by the usable share: 1 for LiFePO4, 0.5 for lead-acid.
A refrigerator and a CPAP machine through an inverter come to about 2,520 Wh a day at the battery. Two days without power needs about 5,040 Wh of LiFePO4 (420 Ah at 12 V) or twice that in AGM. None of the six power stations above covers two days of that on one charge; the 4,096 Wh DELTA Pro 3 gives about 1 day 15 hours. Switch the calculator to What size I need to check your own list and the solar panels that would refill it.
Worked examples
Camping with a CPAP on a 100 Ah battery
A CPAP machine (ResMed AirSense 11, 56.1 W typical) and a 40 W fan, 8 hours a night each, through an inverter on a 12 V 100 Ah battery:
- Devices: 56.1 × 8 + 40 × 8 = 769 Wh a day, an average of 32 W.
- At the battery: 32 ÷ 0.9 + 6 = 41.6 W.
- LiFePO4: 1,200 Wh ÷ 41.6 W = about 29 hours: one full day and night, with a little to spare. AGM, used to 50%: about 14.4 hours, not quite a full day.
Running the CPAP from a 12 V DC adapter instead of the inverter, or switching the inverter off between uses, saves its loss and idle draw: on lithium the same load then lasts about 1 day 13 hours.
A power cut on a Jackery Explorer 1000 v2
A home refrigerator (617 kWh a year, an average of 70 W) and a CPAP machine for 8 hours come to 2,139 Wh a day. The Jackery’s 1,070 Wh × 0.85 = 910 Wh lasts about 10 hours. The fridge is 79% of that: keeping its door shut matters more than anything else.
A 10,000 mAh power bank
10,000 mAh at 3.7 V is 37 Wh. At 1 A from the cell (3.7 W) it lasts 10 hours. Charging a phone at 5 V and converting the voltage loses some of that, so it fills a phone fewer times than the mAh figures suggest. At 37 Wh it is well under the 100 Wh limit for flying.
Recharging a DELTA 3 Plus from solar in Washington
From 20% to full is 819 Wh. With 400 W of panels at Seattle’s 3.95 peak sun hours, that is about 1,190 Wh a day, so one good day. In December, at 1.32 sun hours, it is about 400 Wh a day: about two days.
Flying with a battery or power bank
Under the FAA’s PackSafe rules, lithium batteries up to 100 Wh are allowed in carry-on, in a device or as a spare; between 101 and 160 Wh you need the airline’s approval and can carry up to two spares; over 160 Wh they are not allowed in passenger baggage at all. Spare batteries and power banks never go in checked bags. Every power station on this page is over 160 Wh. The calculator shows which side of the line a lithium battery falls on.
Data sources and updates
| Input | Source | Vintage |
|---|---|---|
| LiFePO4 usable share, efficiency, charge rate, temperatures | Battle Born Batteries BB10012 data sheet | Retrieved October 2026 |
| Lead-acid depth of discharge, cold capacity, charging | Trojan Battery Battery Maintenance and User’s Guide (2023); T-105 and 8D-AGM ratings | 2023; retrieved October 2026 |
| Inverter loss and idle draw | Victron Energy Phoenix Inverter VE.Direct 250–800 VA data sheet | Retrieved October 2026 |
| Power station capacity, output and charging | EcoFlow, Jackery, Anker and BLUETTI product specifications | October 2026 |
| Power station usable share (85%) | Jackery’s published runtime formula | October 2026 |
| Peak sun hours and solar yield by state | NREL PVWatts v8 (the lab now called NLR), one reference city per state | Typical-year weather |
| Device watts | EIA RECS 2020 (refrigerator, freezer), ResMed AirSense 11 User Guide (CPAP), Honda wattage guide (others) | 2020; 2023; October 2026 |
Every figure is stored in the GreenCalculus MasterBrain with the exact line it was read from; the calculator reads the live values and shows each one under View calculation detail. Power station specifications are re-checked every three months, because makers revise their pages and replace models.
Frequently asked questions
A 12 V 100 Ah battery holds 1,200 Wh. A lithium (LiFePO4) one runs a 100 W load for about 12 hours and a 60 W load for about 20 hours. An AGM battery, used to the recommended 50%, runs 100 W for about 5.4 hours and 60 W for about 10 hours. Through a 120 V inverter, allow about 10% less plus the inverter’s own draw.
Multiply the amp-hours by the voltage to get watt-hours, multiply by the share you can use (all of a lithium battery, half of a lead-acid one), then divide by the load in watts. A 12 V 50 Ah lithium battery (600 Wh) running a 30 W load lasts about 20 hours.
A typical US main refrigerator uses 617 kWh a year, an average of about 70 W. A 1,000 Wh-class power station such as the Jackery Explorer 1000 v2 (1,070 Wh, 85% usable) runs it for about 13 hours, and a 4,096 Wh EcoFlow DELTA Pro 3 for about 2 days. An older or larger fridge uses more.
ResMed gives a typical power use of 56.1 W for the AirSense 11 with its power supply. Through an inverter, a 12 V 100 Ah lithium battery runs it for about 17.5 hours, two 8-hour nights. A 1,070 Wh power station runs it for about 16 hours. Without the humidifier it uses less.
From 20% to full on a 10 A charger, about 8 hours for lithium or AGM. A 20 A charger takes about 4 hours for lithium and 5 hours for AGM, which charges at full speed only to 80% and then tops up for up to 2 hours. A lithium battery accepts up to 50 A (0.5C), about 1.6 hours.
Refilling a 12 V 100 Ah lithium battery from 20% (960 Wh) in one average day takes about 250 W of panels in Texas, at 5.22 peak sun hours, and about 330 W in Washington. In December it takes about 370 W in Texas and close to 1,000 W in Washington.
Wh = mAh ÷ 1,000 × volts. Phone and power bank capacities are quoted at the 3.7 V cell, so 10,000 mAh is 37 Wh and 20,000 mAh is 74 Wh.
Power banks up to 100 Wh go in carry-on, never checked bags. From 101 to 160 Wh you need the airline’s approval. Over 160 Wh, which includes every portable power station on this page, lithium batteries are not allowed in passenger baggage on US flights (FAA PackSafe).
It describes how a lead-acid battery gives fewer amp-hours when it is discharged faster. Runtime = rated hours × (capacity ÷ (rated hours × current)) to the power k. From Trojan’s published ratings, k is about 1.16 for a flooded battery and 1.22 for an AGM. Lithium batteries are close to 1, so they are not corrected.
Methodology notes and limitations
Device figures. The refrigerator and freezer use EIA’s average yearly use for homes that have one, spread over the day. The CPAP is ResMed’s typical figure. Other devices use Honda’s running watts, a generator-sizing figure that is often higher than what a device draws in use; they are marked in the results. Enter your own figures where you have them.
Peukert correction. Applied to lead-acid only, with exponents derived from one flooded and one AGM battery’s 5-hour and 20-hour ratings, and never above the 20-hour rating. For a list of devices it uses the average current, which understates the loss when a big load runs in short bursts.
Cold. Lead-acid capacity follows a straight line between Trojan’s two published points, 50% at 0°F and 100% at 80°F. No capacity loss is applied to lithium, for which no comparable figure is held; the calculator warns when it is too cold to charge or discharge.
Charging. Power stations are timed at their makers’ maximum input; real charging slows near full. Lead-acid absorption time is Trojan’s maximum, so it may finish sooner.
Solar. Sun hours are for one reference city per state with the panel tilted 20° facing south; the 0.75 ratio comes from the same PVWatts run.