How many watts can you pull from a 12V battery?

The maximum continuous watts depends on the battery's discharge rate and your wiring. Battle Born prints "100 Amps Continuous" for its 100Ah 12V LiFePO4, which is 1,280W at the 12.8V nominal Victron prints for that chemistry. Lead-acid can supply more current than people expect but gives back far less energy for it: Power-Sonic publishes a 1-hour rate of 60.0A for its PDC-121000, a 12V 100Ah AGM, and a constant-power table that gives 177.3W per cell for 30 minutes at its 1.75 volts-per-cell end point, which is 1,064W across the battery's six cells. The catch is on the same sheet, which rates that battery 100.0Ah at the 20-hour rate and only 60.0Ah at the 1-hour rate, so pulling harder buys you current and costs you capacity.

Do I need an inverter with a 12V battery?

Only if you are running AC devices (anything with a standard wall plug). 12V DC devices like RV fridges, LED strips, USB chargers, and water pumps connect directly to the battery, skipping the inverter and its conversion loss entirely. Victron prints a maximum of 87-92% for its small Phoenix inverters, and its measured curve for a 3kVA unit reads 71% at a 50W load, so the loss is about 8% at best and much larger when a big inverter runs a small load. For mixed setups, run as many devices on DC as possible and only use the inverter for things that require 120V AC like a coffee maker or microwave. If you need automatic switchover during a power outage, a UPS backup time calculator estimates how long a UPS keeps your equipment running.

Is a 12V 100Ah battery the same as a 12V 100Ah battery of a different brand?

Not necessarily. Two batteries with identical labels can perform very differently. A premium LiFePO4 cell from a reputable manufacturer delivers consistent capacity across temperatures and discharge rates. Cheaper cells can fall short of their label, and they fall furthest under higher loads or in cold weather. Internal resistance varies between makes too: lower resistance means more usable power and less heat thrown away. Where the maker publishes a discharge table, that table is the honest capacity figure, not the number on the front of the case.

Does a 100Ah AGM really give half the runtime of a 100Ah LiFePO4?

Close to it, and for two separate reasons. The first is depth of discharge: Concorde recommends no more than 50% for AGM while Battle Born prints 100% as usable for LiFePO4, so the same label starts with half the energy on the table. The second is rate: an AGM returns less than its rated amp-hours as the draw rises, while LiFePO4 holds its rating to a 1C draw. At 50W this calculator gives a 100Ah AGM 10.7 hours against 18.4 for LiFePO4, and at 100W it gives 4.8 against 9.2.

12V Battery Runtime Calculator — By Chemistry

7 min read

To find 12V battery runtime, pick your battery chemistry first, then enter capacity, load, depth of discharge and system efficiency. A 100Ah 12V LiFePO4 battery holds 1,280Wh at the 12.8V nominal Victron prints for it, 1,024Wh of that at 80% depth of discharge, and 922Wh after a 90% system efficiency: 18.4 hours at 50W, 9.2 hours at 100W, or 1.8 hours on a 500W inverter load. The same 100Ah label in AGM, at the 50% depth Concorde recommends, gives 10.7, 4.8 and 46 minutes, because a lead-acid battery returns less of its rating the harder you pull. Those lead-acid figures come from a rate correction fitted to the discharge tables Trojan, Lifeline and Victron print for their own batteries, which it reproduces within about 10% for flooded, 6% for AGM and 2% for gel. Voltage is locked at 12V, the most common battery voltage for RVs, boats, camping setups and off-grid solar.

Key 12V battery runtime figures at 25W and 100W loads with lead-acid depth of discharge.

How Long Will a 12V Battery Last? Runtime by Chemistry and Load

Chemistry moves this answer more than anything else on the page. A flooded, AGM or gel battery hands back less of its label capacity the harder you pull, so a 100Ah battery is only a 100Ah battery at the 20-hour rate its label was measured at. A LiFePO4 battery holds its rating up to a 1C draw and sits at 12.8V nominal rather than 12V. This chart runs a 100Ah 12V battery at each chemistry's maker-printed depth of discharge and 90% system efficiency:

Load	Flooded, 50% DoD	AGM, 50% DoD	Gel, 50% DoD	LiFePO4, 80% DoD
25W	22.9 hours	23.8 hours	24.8 hours	36.9 hours
50W	10.3 hours	10.7 hours	10.8 hours	18.4 hours
100W	4.6 hours	4.8 hours	4.7 hours	9.2 hours
300W	1.3 hours	1.4 hours	1.3 hours	3.1 hours
500W	43 min	46 min	42 min	1.8 hours

Battery size still scales the answer, but not the way most charts imply. LiFePO4 scales straight: at 100W, 50Ah gives 4.6 hours, 100Ah gives 9.2 and 200Ah gives 18.4. AGM does better than straight, because a bigger battery is also a gentler draw per amp-hour: at the same 100W, 50Ah gives 2.2 hours, 100Ah gives 4.8 and 200Ah gives 10.7, so doubling capacity multiplies runtime by about 2.2 rather than 2. If your bank is AGM rather than lithium, our AGM runtime calculator starts from AGM defaults instead.

The cells at the far corners of the chart sit outside the range of discharge points the correction was fitted to: the 25W and 50W AGM and gel figures are lighter than the 20-hour rate the printed tables begin at, and every 500W figure is heavier than they end at. The calculator says so on screen when your own numbers land there. Running loads on 12V DC without an inverter removes the conversion stage entirely, which leaves only wiring loss and stretches every figure above.

12V battery runtime chart for common loads including LED lights, phone charger, fan, and mini fridge. — Common 12V loads on a 100Ah LiFePO4 at 80% DoD and 90% efficiency; the same label in AGM runs a little over half as long.

What Can a 12V Battery Power?

Device	Typical Watts	Runtime on 100Ah LiFePO4 (80% DoD)
LED light strip (1m)	5-15W	61-184 hours
Phone charger	10-18W	51-92 hours
Laptop charger	45-65W	14-20 hours
12V compressor fridge	30-60W avg	15-30 hours
CPAP machine	30-60W	15-30 hours
Portable fan	15-40W	23-61 hours
Water pump (RV)	40-100W	9-23 hours
Inverter + TV (32")	50-80W	11-18 hours

Typical wattages are our own estimates; check your appliance's nameplate.

Runtimes above are for a 100Ah 12V LiFePO4 battery at 80% DoD and 90% system efficiency, which delivers 922Wh. The same 100Ah label in AGM at 50% DoD delivers a little over half as long at these loads, and every figure falls further in the cold.

Example: Weekend Camping with a 12V Battery

Scenario: you are car camping for two nights with a 100Ah LiFePO4 battery. Two days of loads look like this:

LED lights — 10W for 5 hours a night = 100Wh over two nights
Phone charging (2 phones) — 20W for 3 hours a night = 120Wh
12V fridge — 40W average, running 48 hours = 1,920Wh
Portable speaker — 5W for 6 hours a night = 60Wh

Total weekend energy: 100 + 120 + 1,920 + 60 = 2,200Wh. Your 100Ah 12V LiFePO4 battery stores 1,280Wh, 1,024Wh of that at 80% DoD, and 922Wh after the 90% system efficiency the calculator applies. That leaves you 1,278Wh short, and the fridge is almost all of it.

Check any remedy against that number rather than against instinct. A second identical battery at 80% DoD brings you to 1,843Wh, which is still 357Wh short. Battle Born prints 100% depth of discharge for its LiFePO4, and two batteries taken to full depth deliver 2,304Wh, which covers the weekend with about 100Wh spare. The cheaper fix is the fridge: at the 40% duty cycle our worked example below uses, a 50W compressor averages 20W, the fridge drops from 1,920Wh to 960Wh, and two batteries at 80% DoD cover the weekend with 600Wh to spare. A portable solar panel helps as well, though how much it makes in a day depends on the panel, the season and the sky.

Worked Examples

Running a 12V Compressor Fridge While Camping

Context

Your 12V compressor fridge draws 50W when the compressor runs and cycles about 40% of the time (effective 20W average). You have a 100Ah 12V battery and want at least 24 hours before needing a recharge.

Calculation

Usable at DoD = 100 x 12.8 x 0.80 = 1,024 Wh; delivered = 1,024 x 0.95 = 972.8 Wh

Runtime at 20W average = 972.8 / 20 = 48.6 hours

Interpretation

At 20W average draw, you get two full days from a single 100Ah battery. Even at the full 50W continuous, you still get more than 19 hours. The 12.8V nominal Victron prints for LiFePO4 is worth 6% of that on its own.

Takeaway

Duty cycle makes all the difference for fridges. For a more detailed refrigerator-specific analysis, use our 12V fridge runtime calculator which accounts for duty cycle directly.

Powering a Portable Ham Radio Station

Context

You operate a portable HF radio that draws 120W on transmit and 20W on receive. During a field day event, you estimate 30% transmit time (effective average ~50W). You have a 100Ah AGM at the 50% DoD Concorde recommends.

Calculation

Current drawn = 50W / 0.95 / 12V = 4.39A, which is 0.044C against the 100Ah 20-hour rating

AGM rate correction: a full discharge at 0.044C = 22.9 hours; at 50% DoD that is 11.4 hours

Interpretation

11 hours covers a typical field day event. If you transmit more heavily, runtime drops faster than the wattage rises: at a full 120W continuous transmit the battery lasts 4.2 hours, not the 4.8 that a flat energy sum would predict.

Takeaway

For multi-day events, bring solar to recharge between sessions. Figure out what size panel you need with our solar panel size calculator.

Frequently Asked Questions

Glossary

Duty Cycle

The percentage of time a device actually runs during its operating period. A fridge compressor with a 40% duty cycle runs 24 minutes per hour. Effective power draw equals rated wattage multiplied by the duty cycle.

DC Efficiency

Running 12V devices straight from a 12V battery skips the inverter, so there is no conversion stage to lose anything in and only wiring resistance remains. Through an inverter you keep most of the energy and lose the rest: Victron prints a maximum of 87-92% for its small Phoenix inverters, so about 8-13% goes as heat at best. At light load it is far worse, and Victron's own measured curve for a 3kVA unit reads 71% at 50W.

Nominal Voltage

The standard voltage used to name a battery system rather than a voltage you will read at the terminals. Power-Sonic calls its PDC-121000 a 12.0 volt battery of six cells, then prints discharge end points that fall as the rate rises: 10.8 volts at the 20-hour rate, 10.2 at the 5-hour rate and 9.6 at the 1-hour rate. LiFePO4 is named differently again, because Victron prints "Nominal voltage 12,8 V" and 1,280Wh of nominal energy for a 100Ah cell block, so this calculator uses 12.8V when you pick LiFePO4 and 12V for the three lead-acid chemistries.

Discharge Rate (C-rate)

The current you are drawing expressed as a fraction of the 20-hour rating. A 100Ah battery supplying 5A is at 0.05C, the rate its label was measured at; 50A is 0.5C. Lead-acid capacity falls as C-rate rises, which is why this calculator shows the C-rate beside the result and says so when your figure runs past the range the printed tables cover.

Recharging with solar? Our solar battery charge time calculator shows how long your panels take to refill a 12V battery.

A 12V system is the simplest and most versatile battery setup for portable and mobile use. Match your battery capacity to your actual load — not your worst-case fantasy load — and you will avoid both overspending and running out of power at 2 AM. When the goal shifts from camping to keeping a household fridge running through a grid-down event, our 12V battery for fridge during power outage guide applies the same Wh math to an extended-outage scenario. For non-12V portable devices, we also have dedicated calculators for drone flight time and e-bike battery range.

More Battery calculators

Browse all battery calculators — LiFePO4, lead-acid, AGM, and lithium-ion runtime, charge time, and capacity sizing.

Last updated: September 23, 2026

Written and maintained by Dan Dadovic, Commercial Director at Ezoic Inc. & PhD Candidate in Information Sciences. He works professionally as Commercial Director at Ezoic Inc., leading revenue strategy across digital publishing.

Disclaimer: Calculator results are estimates based on theoretical formulas. Actual performance varies with temperature, battery age, load patterns, and equipment condition. For critical electrical work, consult a licensed electrician.

Methodology reviewed by Doc. dr. sc. Damir Topić, Assistant Professor, FERIT Osijek.