How Long Will 100ah Battery REALLY Last? (Explained!)

How long will 100ah battery last on a load? Let's find out!

Most search results for 100Ah battery runtime will provide a “theoretical” estimate. Yet, real-world results may differ.

In this article, I'll share techniques (based on my experience with batteries and their discharge mechanisms) for determining the most accurate estimated runtime for your 100Ah battery.

Looking for an effortless solution? Try our battery runtime calculator.

how long will 100ah battery last calculator

Battery Capacity
Battery Voltage
Battery Type
Battery State of Charge (SoC)
Recommended Battery Depth of Discharge Limit (DoD)
Load Connected through inverter?
Total Load (in watts)

For most accurate estimate: Use this calculator for loads of up to 250W with 12V 100Ah lead acid and up to 600W with 12V 100Ah lithium-ion. I'll explain the reason later in this article.

calculator Assumptions

  • The result takes into account the efficiency of an inverter (90%) and the efficiency of the battery discharge (lead acid: 85%, Lithium: 95%).

Depth of Discharge (DoD) measures the used capacity of your battery from its total capacity. Lead-acid, AGM, and gel batteries should not be discharged below 50%, while only lithium (LiFePO4) batteries can be safely depleted to 100%.

Battery state of charge (SoC) refers to the amount of charge it has relative to its total capacity. A fully charged battery has an SoC of 100%.

Example: How Long Will A 100ah Battery Run An Appliance That Requires 400 Watts?

Let's suppose...

  • Battery capacity: 100ah
  • Battery voltage: 12v
  • Battery type: Lithium
  • Battery state of charge: 100% charged
  • Battery depth of discharge limit: 100%
  • Load connected through the inverter? Yes
  • Total load: 400 watt
how long will 100ah battery last
My 12v 100ah LiFePO4 battery

Summary: 12v 100ah lithium battery will last about 2 hours and 30 minutes running an appliance that requires 400 watts.

5 Steps To Calculate 100ah Battery Runtime

Follow these steps to calculate 100ah battery life/backup time on a load.

1. Calculate the battery capacity in watts

Watt is a measurement unit for total energy (watt = amps × volts). Using watts to measure the battery capacity will make it easier --- because most home devices have their power listed in watts.

Also, you can find out how much ACTUAL energy your battery can store using this method.

For example: A 24V 100Ah battery has the capacity to store twice as much power as a 12V 100Ah battery.

Formula: Battery watt-hours = Battery (Ah) × Battery Volts

For calculation, let's say you have a 12v 100ah battery.

100ah battery in watt-hours = 100 × 12 = 1200 watt-hours 

2. Consider the battery Depth of Discharge

Multiply the battery capacity in watt-hours by the battery depth of discharge limit.

Depth of Discharge measures the amount of energy taken from the battery and how much remains. A high DoD shows that you have used more energy from the battery, while a low DoD means you have used less.

Default battery depth of discharge limit:

  • Lead-acid battery: 50% DoD limit
  • Lithium: 100% DoD limit

Let's say you have a lead acid battery.

Battery capacity in wh after DoD limit = 1200 × 50% = 600wh

3. Consider the discharge efficiency rate

Multiplying the battery capacity after DoD by 0.85 for lead acid and 0.95 for lithium-ion.

Unfortunately, batteries are not 100% efficient when discharging. The efficiency rate will depend on many factors, including — how heavy the load is, battery chemistry (lead acid vs lithium), battery temperature, and self-discharge rate.

Based on data:

  • Lead-acid batteries discharge efficiency ≈ 80 − 85%
  • Lithium-ion batteries discharge efficiency ≈ 90 − 95%

I'll carry on with a lead acid type battery.

Battery capacity after discharge efficiency = 600 × 0.85 = 510wh

4. Consider the inverter efficiency

Multiply the battery capacity after the DoD limit with the inverter efficiency rate.

Batteries store power in DC (direct current) but most of our household appliances need AC (alternating current). So to run appliances, you need an inverter that will convert the DC into AC.

Unfortunately, inverters are not 100% efficient. Most of them are about 90% efficient.

Battery AC watts = 510 × 90% = 460 AC watt-hours 

5. Final step (calculation)

Divide the battery AC watt-hours by the Total load connected. Let's say 100 watt appliance is connected to your 100ah battery.

100ah battery runtime on 100w appliance = 540 ÷ 100 = 4.6 hours

How long will a 100ah battery run an appliance that requires 100w? 12v 100ah lead-acid battery will run an appliance that requires 100w for about 4 and a half hours.

Now let's discuss some shortcomings and drawbacks of these methods.

The Problems and Shortcomings of These Strategies

Here are some extra yet important factors to consider when figuring out how long your 100Ah battery will last running load.

1. Battery Life

Every time you charge and discharge a battery to its Depth of Discharge (DoD) limit, its storage capacity decreases, known as a cycle.

If you have used your battery for a few hundred cycles, then the result will be different. This factor isn't included in my above-given methods.

Lead acid batteries lose 20% of their charge-holding capacity after 500 cycles. And lithium batteries at 2000 cycles (ask your manufacturer to get the most accurate number).

2. battery discharge mechanism

Especially, lead-acid batteries are designed to be discharged in 20 hours to maintain battery health and optimize efficiency. For example, it's recommended to discharge a 100Ah lead-acid battery at 5 amps.

But, AGM and lithium (LiFePO4) batteries can handle a higher discharge rate (usually, 50% of their capacity). Ask your manufacturer to get the most accurate number.

If you take the power out of your battery too fast, it will get hot inside and lose some of its power. This factor isn't included in the above methods.

For example, if you discharge your lead-acid battery with 100 amps, Theoretically it should last 30 minutes (keep in mind the 50% DoD limit) but may last about 10 → 15 minutes.

Check the battery discharge rate on its specs sheet or it'll be mentioned on the battery (1h → 1C, 2h → 0.5C, 5h → 0.2C, etc).

Related: Battery Charge And Discharge Rate Calculator: C-Rating To Amps

3. external battery temperature

Batteries perform their best at room temperature. The temperature at which batteries operate the best is 68ºF or 20ºC (Ask your manufacturer to get the most accurate number).

A higher or lower temperature (than what's recommended) will affect the battery's performance. A rule of thumb is "an increase of temperature to 77ºF or 25º C can reduce battery performance by 50%".

tips to increase battery efficiency

Here are some tips to increase the performance/efficiency of your batteries.

  1. Choose the right size wire from the battery to the inverter. The size of the wire will depend on the load. The higher the load is, the thicker wire you need.
  2. Store your battery in the recommended temperature range. Usually, it is between –20°C to 50°C for lead acid and –20°C to 60°C for lithium-ion.
  3. Do not discharge your battery at a higher rate. The max discharge rate should be — Lead-acid; 25% of its total capacity, Lithium battery; 50% of its full capacity.

Read this if you have multiple 100ah batteries

If you have multiple 100ah batteries, you can connect them in series, parallel, or series-parallel.

Series vs parallel connection:

  • Series: This will add up the voltage but the amps will stay the same. 2x 12v 100ah batteries connected in series will be equal to 24v 100ah.
  • Parallel: This will add up the amps but the voltage will stage the same. 2x 12v 100ah batteries connected in series will be equal to 12v 200ah.

Series vs parallel connection — which one is best for you? Your first priority should be the series connection. A high-voltage system will increase wiring efficiency. But make sure "your inverter should support 24v input".

If you have a 12v inverter, use a parallel connection but thicker wiring from battery to inverter.

If you have more than 2 batteries, use a series-parallel connection.

Note: To maximize the power, when connecting multiple batteries they should be the same capacity, voltage, brand, and age.

How Long Will A 100ah Battery Last?

Here are charts on how long will a 12v 100ah lead acid and lithium battery will last while running different watt appliances.

How Long Will 100ah Lead-Acid Battery Last?

Appliance Power Required100ah Lead Acid Battery Runtime
20 watt23 hours
40 watt11.5 hours
50 watt9.2 hours
60 watt7.7 hours
100 watt4.5 hours
150 watt3 hours
200 watt2.3 hours
300 watt1.5 hours
400 watt1.16 hours
500 watt45 - 55 minutes
600 watt35 - 45 minutes
800 watt25 - 35 minutes
1000 watt15 - 27 minutes
1200 watt12 - 23 minutes
1500 watt10 - 18 minutes
2000 watt7 - 13 minutes
3000 watt5 - 9 minutes


  • 100ah lead acid battery will last anywhere between 20 hours to 1 hour. The exact time will depend on the size of the load.

How Long Will 100ah Lithium (LiFePO4) Battery Last?

Appliance Power Required100ah Lithium Battery Runtime
20 watt52 hours
40 watt26 hours
50 watt21 hours
60 watt17 hours
100 watt10 hours
150 watt7 hours
200 watt5 hours
300 watt3.5 hours
400 watt2.5 hours
500 watt2 hours
600 watt1.7 hours
800 watt1.3 hours
1000 watt1 hour
1200 watt40 - 50 minutes
1500 watt30 - 40 minutes
2000 watt20 - 30 minutes
3000 watt10 - 20 minutes


  • 100ah lithium battery will last anywhere between 50 hours to 30 minutes. The exact value will depend on the size of load.

100Ah battery runtime: FAQ's

A 12v 100Ah lead-acid battery with 50% depth of discharge will run a small size camping fridge (2-5 cu. ft.) for about 18-24 hours.

A 100ah battery will run a Tv for about 10-50 hours. The exact value will depend on the size and type of television, and also the battery depth of discharge limit.

You can safely run 600 watts on a 100ah lithium battery at a time and 250 watts on a 100ah lead-acid battery.

100ah lead-acid battery can run a 100 watt of lights for about 6 hours.

100ah battery is equal to 1200 watt-hours and you can run almost any all kind of home appliances with it, like fridge, tv, charging phone, laptop, lights, etc…

A 100ah battery would be enough for camping to run most of the basic appliances like lights, charging phones and laptops, etc…

12v 100ah means 1200 watts, 24v 100ah means 2400 watts, 48v 100ah means 4800 watts. To calculate the watts in a battery, use this formula (battery watts = battery amp-hours * battery volts).

12v 100ah lithium battery will run an appliance that requires 1000w for about 1 hour.

12v 100ah lithium battery will run an appliance that requires 800w for about 1 hour and 15 minutes.

12v 100ah lithium battery will run an appliance that requires 200w for about 5 hours.

12v 100ah lithium battery will run an appliance that requires 600w for about 1 hour and 40 minutes.

12v 100ah lithium battery will run an appliance that requires 40w for about 26 hours.

12v 100ah lithium battery will run an appliance that requires 500w for about 2 hours.

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Chris Tsitouris is a renewable energy professional with 10+ years of experience as Director of Engineering at Solar Spectrum, previously working as Project Manager at SunPower and Energy Analyst at the National Renewable Energy Laboratory. As a thought leader, Chris has authored numerous articles and research papers.

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