Battery Runtime Calculator: How Long Does Battery Last?

How long will your battery last? find out with our easy-to-use battery runtime calculator.

Battery runtime calculator

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

Note: Use our solar panel size calculator to find out what size solar panel you need to recharge your battery in desired hours.

Calculator assumptions

  • This calculator will take into account the efficiency of an inverter (90%) and the efficiency of the battery discharge (lead acid: 85%, Lithium: 95%).

Limitations of this calculator

  • Please note that the calculator doesn't include Peukert's law, temperature, and battery age in its calculations, which can affect the battery's discharge time. But it can give you a close estimated runtime.

How to use our battery runtime calculator?

1. Enter battery capacity in amp-hours (Ah): If the battery capacity is mentioned in watt-hours (Wh), Divide the watt-hours by battery voltage (V) to find out the battery capacity in Ah.

2. Enter your battery voltage (V): Do you have a 12v, 24, or 48v battery? For a 12v battery, ENTER 12.

3. Select your battery type: For lead acid, sealed, flooded, AGM, and Gel batteries select "Lead-acid" and for LiFePO4, LiPo, and Li-ion battery types select "Lithium".

4. Enter your battery's state of charge (SoC): SoC of a battery refers to the amount of charge it has relative to its total capacity. A fully charged battery will have 100% SoC.

5. Enter your battery's recommended depth of discharge (DoD) limit: Battery depth of discharge (DoD) measures the used capacity of your battery from its total capacity.

Lead-acid, AGM, sealed, flooded, and Gel batteries should not be discharged below 50%, while only lithium (LiFePO4, LiPo, and Li-ion) batteries can be safely depleted to 100%. Ask your manufacturer or have a look on at your battery's specs sheet for a more accurate value.

6. Is your load connected through an inverter? Select yes, if you're using an inverter to run the AC appliances. Or select no, if the appliance is directly connected to the battery without an inverter (which is usually not recommended).

6. Enter total output load in watts: If your appliance has an output load mentioned in amps, convert it into watts by multiplying the amps by the given volts of appliance.

Enter "Calculate Battery Runtime" button to get the result.

2 ways to calculate battery runtime

Ready for calculation? Let's dive in! I'll share 2 methods to estimate battery life from basic (least accurate) to advanced (most accurate).

Formula 1

Formula: Battery capacity in Ah  ÷ Output amps (A)

Or,

Battery runtime = Battery capacity in watt-hours (Wh) ÷ Total Output in watts 

Accuracy: Lowest

Dividing the battery capacity (in amp-hours - Ah, or milliamp-hours - mAh) by the output load (in amps - A, or milliamps - mAh) is the least accurate way to calculate the battery runtime.

Because it doesn't take into account for battery's discharge efficiency rate, recommended depth of discharge, and state of charge.

Mostly, the battery capacities are mentioned in amp-hours (Ah) but our appliances in watts. Which makes it confusing in the first place. You can convert the battery capacity in watt-hours or the appliance input capacity into watt-hours to make it work.

Battery capacity in watt-hours = Battery Ah × Battery voltage

Output load in load in amps = Load in watts ÷ volts

Example

Let's say you have:

  • Battery capacity: 50Ah
  • Output load: 10A

To calculate 50ah battery lifetime using this formula, divide 50ah by 10a.

50ah ÷ 10a = 5 hrs

According to this formula, a 50ah battery will run a 10-amp load for 5 hours.

formula 2

Formula: Battery runtime = (Battery Ah × Battery volts × discharge efficiency × DoD limit × SoC × inverter efficiency) ÷ load

Accuracy: Highest

This formula takes into account for battery's discharge efficiency rate, recommended depth of discharge, and state of charge.

Based on directscience.com data:

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

Example

Let's continue with the previous example and find out the most accurate runtime estimate.

Let's say you have:

  • Battery capacity: 50Ah
  • Battery voltage: 12V
  • Battery type: Lead acid
  • Battery SoC: 100% (fully charged)
  • DoD limit: 50%
  • Running load through an inverter? Yes (inverter efficiency - 90%)
  • Output load: 120 watts (10 amps @ 12v)

Now let's put this info into our 2nd formula.

 (50ah × 12v × 85% × 50% × 100% × 90%) ÷ 120 watt
 (229.5) ÷ 120 watt = 1.9 hours

Turns out, in actuality a 50ah battery will run a 10A load for about 1.9 hours.

That's it! Easy right?

Now let's have a look at why these methods only give estimates, not 100% accuracy.

Why none of these methods guarantee 100% accuracy?

Battery runtime formulas aren't fully accurate due to the complexity of battery discharge, as there are other factors that can impact discharge time. Which are...

1. Batteries discharge unevenly

If you discharge a battery too quickly, it won't provide as much energy as the label claims, known as Peukert's law. This is because more energy turns into heat instead of powering devices when discharged quickly.

The effect of Peukert's law on Lead-acid vs Lithium: Lead acid batteries lose energy faster when discharged quickly, while lithium batteries can be discharged at up to 50% of their capacity without losing power.

Here's an example of how discharge time affects the usable capacity of 100ah lead acid battery.

Usable 100ah lead acid battery capacityHours of discharge
100ah20 hours
90ah10 hours
87ah8 hours
82ah6 hours
80ah5 hours
70ah3 hours
60ah2 hours
50ah1 hour
Note: This table doesn't take into account lead acid's 50% DoD limit.

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

2. Battery life cycles matter

Batteries can only be charged and discharged for a limited number of times, which is called the life cycle.

Lead-acid batteries last for a few hundred cycles if they are maintained properly. Lithium batteries can last for thousands of cycles. But as batteries are used and charged more, they hold less charge capacity.

After about 500 cycles, a lead-acid battery will lose about 20% of its capacity, while a lithium battery will 20% of its capacity after about 2000 cycles. Check your battery's data sheet for more accurate numbers.

3. Effect Of Temperature On Batteries performance

Temperature affects how well your battery works. Usually, batteries work best when it's between 68°F and 77°F (20°C to 25°C).

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

To get the most out of your battery, keep it at the right temperature by using a cooling system or putting it in a spot where it won't get too hot or too cold.

That's it!

Now I'll show you tables and charts showing battery runtime for different voltage (v) and capacities under various loads.

how long Does a 12v battery last?

Here's a chart on how long 12v different amp-hour (Ah) batteries will last running a 10-watt load.

Battery Size (Ah)Runtime (Lead-acid)Runtime (Lithium)
6ah3 hrs6 hrs
7ah3 hrs7 hrs
12ah6 hrs12 hrs
18ah8 hrs19 hrs
20ah9 hrs21 hrs
36ah17 hrs37 hrs
50ah23 hrs52 hrs
60ah28 hrs62 hrs
70ah32 hrs73 hrs
80ah37 hrs83 hrs
100ah46 hrs104 hrs
120ah56 hrs124 hrs
150ah70 hrs155 hrs
200ah93 hrs207 hrs
Table 1: how long will 12v battery last?

summary

  • A 12v battery will last anywhere between 5-20 hours while running a load.

how long will a 24v battery last?

Here's a chart on how long will a 24v different capacity lead acid and lithium (LiFePO4) battery will last running a 100 watts of AC load.

24v Battery CapacityBattery TypeEst. Runtime on 100-watt appliance
100ahLead-acid9 hours
200ahLead-acid18 hours
300ahLead-acid28 hours
400ahLead-acid37 hours
100ahLithium (LiFePO4)21 hours
200ahLithium (LiFePO4)41 hours
300ahLithium (LiFePO4)62 hours
400ahLithium (LiFePO4)83 hours
Table 2: how long will 24v battery last?

summary

  • 24v lead-acid battery will last between 10 to 30 hours while running a 100-watt AC load.
  • 24v Lithium (LiFePO4) battery will last between 20 to 80 hours while running a 100-watt AC load.

Full article: How Long Does A 24 Volt Battery Last? 

How long will a 48V battery last?

Here's a chart on how long will 48v different amp-hours (Ah) battery will last on a 500-watt load.

48v battery capacityBattery typeEst. Runtime (hrs)
100Lead acid4 hrs
200Lead acid7.5 hrs
300Lead acid11 hrs
400Lead acid15 hrs
600Lead acid22 hrs
100Lithium (LiFePO4)8 hrs
200Lithium (LiFePO4)16.5 hrs
300Lithium (LiFePO4)25 hrs
400Lithium (LiFePO4)33 hrs
600Lithium (LiFePO4)50 hrs
Table 3: how long will 48v battery last?

Summary

  • 48v lead acid battery will last anywhere between 4 hours to 22 hours while running a 500-watt load.
  • 48v lithium battery will last anywhere between 8 hours to 50 hours while running a 500-watt load.

how long 70ah battery last?

ApplianceWattage consumptionHow long will a 70ah lead-acid battery last
Fridge300 watts1 hour
TV60 watts5 hours
Trolling motor720 watts20 minutes
Ceiling Fan120 watts2.5 hours
Computer300 watts1 hour
LED Bulb20 watts16 hours
Dishwasher1800 watts10 minutes
Toasters1200 watts16 minutes
Table 4: how long will 70ah battery last?

summary

  • 70ah battery will last anywhere between 15 hours to 15 minutes running different appliances.

Full article: How Long Will 70Ah Battery Last? (In Real World Conditions)

how long will 110ah battery last?

Here are charts on how long will a 12v 110ah lead acid and lithium battery will last on load.

12v 110ah lead acid battery

Appliance Power Required110ah Battery Runtime
50 watt 10 hours
100 watt5 hours
150 watt3 hours
200 watt2.5 hours
300 watt1.5 hours
400 watt1.2 hours
500 watt1 hour
1000 watt30 minutes
Table 5: how long will 110ah lead acid battery last?

Summary

  • 12v 110ah lead-acid battery with a 50% depth of discharge limit will last between 10 hours to 36 minutes.

12v 110ah lithium battery

Appliance Power Required110ah Battery Runtime
50 watt23 hours
100 watt11 hours
150 watt7.5 hours
200 watt5.5 hours
300 watt4 hours
400 watt3 hours
500 watt2.5 hours
800 watt1.4 hours
1000 watt1 hour
Table 6: how long will 110ah lithium battery last?

summary

  • 12v 110ah lithium (LiFePO4) battery with a 100% depth of discharge limit will last between 23 hours to 1 hour.

how long will 300ah battery last?

Appliance Power Required300ah lead-acid Battery Runtime
50 watt 28 hours
100 watt14 hours
150 watt9 hours
200 watt7 hours
300 watt4.5 hours
400 watt3.5 hours
500 watt2.5 hour
800 watt1.5 hours
1000 watt1.3 hours
1200 watt1 hour
1500 watt55 minutes
2000 watt40 minutes
3000 watt25 minutes
Table 7: how long will 300ah battery last?

Summary

  • A 12v 300ah lead acid battery will last anywhere between 28 hours to 20 minutes.

how long will 600ah battery last?

Here are charts on how long will a 12v 600ah lead acid and lithium battery will last on load.

12v 600ah lead acid battery

Appliance Power consumption600ah lead-acid Battery Runtime
50 watt 55 hrs
100 watt28 hrs
200 watt14 hrs
300 watt9 hrs
400 watt7 hrs
500 watt5.5 hrs
600 watt4.5 hrs
800 watt3.5 hrs
1000 watt2.5 hrs
1200 watt2 hrs
1500 watt1.5 hrs
2000 watt1.2 hrs
3000 watt50 minutes
Table 8: how long will 600ah lead acid battery last?

summary

  • A 12v 600ah lead acid battery will last anywhere between 50 hours to 50 minutes running different watt appliances.

12v 600ah lithium battery

Appliance Power consumption600ah lithium Battery Runtime
50 watt 125 hours
100 watt62 hours
200 watt31 hours
300 watt21 hours
400 watt15.5 hours
500 watt12 hours
600 watt10 hours
800 watt7.5 hours
1000 watt6 hours
1200 watt5 hours
1500 watt4 hours
3000 watt2 hours
Table 9: how long will 600ah lithium battery last?

summary

  • A 12v 600ah lithium battery will last anywhere between 120 hours to 2 hours running different watt appliances.

How long will a 150ah battery last?

Here are charts on how long will a 12v 150ah lead acid and lithium battery will last on load.

12v 150ah lead acid battery

Appliance Power Required150ah Battery Runtime
50 watt 14 hours
100 watt7 hours
150 watt4.5 hours
200 watt3.5 hours
300 watt2 hours
400 watt1.5 hours
500 watt1.2 hours
600 watt1 hour
Table 10: how long will 150ah lead acid battery last?

Summary

  • 12v 150ah lead acid battery will last anywhere between 14 hours to 1 hour running different watt appliances.

12v 150ah lithium (LiFePO4) battery

Appliance Power Required150ah Battery Runtime
50 watt 31 hours
100 watt15 hours
150 watt10 hours
200 watt7.8 hours
300 watt5 hours
400 watt3.5 hours
500 watt3 hours
600 watt2.5 minutes
800 watt2 hours
1000 watt1.5 hours
1200 watt1.3 hours
1500 watt1 hour
Table 11: how long will 150ah lithium battery last?

Summary

12v 150ah lithium battery will last anywhere between 30 to 2 hours running different watt appliances.

how long will 200ah battery last?

ApplianceWattage consumptionEst. runtime (50% DoD)Est. runtime (100% DoD)
Fridge300 watts3 hrs7 hours
TV60 watts15 hrs34 hours
Trolling motor720 watts1.2 hrs2.5 hours
Ceiling Fan120 watts8 hrs17 hours
Computer300 watts3 hrs7 hours
LED Bulb20 watts46 hrs104 hrs
Dishwasher1800 watts30 minutes1 hour
Toasters1200 watts40 minutes1.2 hours
Table 12: how long will 200ah battery last?

summary

  • 12v 200ah lead acid battery will last anywhere between 15 hours to 40 minutes running different appliances.
  • 12v 200ah lithium battery will last anywhere between 34 hours to 1 hour running different appliances.

Conclusion

Calculating battery runtime is a complex process, and there is no one-size-fits-all formula. The accuracy of the results depends on several factors, including battery age, temperature, load, and other external factors.

While our calculator and mentioned formulas can provide a rough estimate, they should not be solely relied upon. It is essential to understand the limitations of these methods and factor in additional variables to ensure that the battery runtime is accurately estimated for the intended use case.

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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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