How Long Will A 50Ah Battery last? (Incl. Runtime Calculator)

I have been using a 50ah battery for over a month now. So in this post, I’ll share how long will a 50ah battery last on various loads.

Additionally, I will share some important factors that can affect the backup time of your 50ah battery but are often overlooked.


A 12v 50ah battery will last anywhere between 1 to 20 hours. The exact runtime will depend on various factors such as battery type, output load, and ambient temperature.

Need an easy solution? Use our battery runtime calculator to find out.

50ah battery runtime 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)

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

Calculator Assumptions

  • This calculator takes 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 is based on estimates and actual results may vary based on factors such as battery health, temperature, and the discharging rate. I will discuss these factors in more detail later in this post.

Battery depth of discharge (DoD) refers to the percentage of the battery’s capacity that has been discharged. It is recommended to limit the depth of discharge to around 50% for lead-acid, AGM, and gel batteries. Lithium (LiFePO4) batteries are an exception, as they can be fully discharged to 100%.

Battery state of charge (SoC) is the level of charge a battery has as a percentage of its total capacity. When a battery is fully charged, it has a state of charge of 100%.

Example: how long will a 50ah leisure battery last?

How long will a 50ah battery last?
Screenshot from the above calculator: How long will a 50ah battery last?

12v 50ah leisure battery with 50% DoD limit last about an hour running 230 watts of AC load.

Note: Must watch this video to understand the basics of batteries (capacity, charge, and discharge mechanism)

5 Steps to calculate 50ah battery runtime

To calculate the runtime of a 50Ah battery on a load, follow these steps:

Step 1. Multiply the battery capacity in amp-hours (Ah) by its voltage (V).

This will give you an idea of how much actual power your battery can store. For example, a 12V 50Ah battery is equal to 600 watt-hours of power, while a 24V 50Ah battery is equal to 1200 watt-hours (or 12v 100ah battery).

Let’s assume you have a 24v 50ah lithium battery.

50ah battery in watts = 50 × 24 = 1200 watt-hours (Wh)

Step 2. Calculate the battery’s usable capacity in watt-hours.

To do that — multiply the battery capacity in watt-hours by its depth of discharge limit.

Default battery depth of discharge limit — Lead-acid battery: 50% DoD limit, Lithium: 100% DoD limit.

24v 50ah lithium battery usable capacity = 1200 × 100% = 1200Wh

Step 3. Multiply the battery’s usable capacity by 0.85 if you have a lead-acid, AGM, or gel battery, or by 0.95 if you have a lithium (LiFePO4) battery.

This step takes into account for battery’s discharge efficiency rate.

Based on data:

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

Now let’s multiply 1200 by 0.95 for a lithium battery.

1200 × 0.95 =  1140Wh or 1.14kWh

Step 4. Multiply the battery’s usable capacity after taking into account its discharge efficiency by the inverter efficiency rate.

The purpose of an inverter is to convert DC power to AC power, which is required for most household appliances. However, most inverters have an efficiency rate of around 90%.

Let’s take a 90% efficient inverter for this calculation.

1140 × 90% = 1020 AC watt-hours 

Step 5. Divide the battery AC watt-hours by the total load connected.

Let’s say a 100-watt appliance is connected to your 24v 50ah LiFePO4 battery

50ah battery runtime on 100w appliance = 1020 ÷ 100 = 10.2 hours

It turns out that a 24V 50Ah lithium battery will last approximately 10 hours when running a 100-watt load.

3 additional factors that will affect 50ah battery runtime

Here are some additional, yet important points to keep in mind when calculating how long your battery will last while running a load.

1. Batteries Discharge Unevenly

If you discharge certain types of batteries, such as lead acid, AGM, gel, and sealed batteries too quickly, they may not provide as much energy as the label claims. This is known as Peukert’s law.

Usually, Lead acid batteries are recommended to be discharged in 20 hours or at a 0.05C rate.

For example, if you discharge a 50Ah lead acid battery at 50 amps, it will not last for 30 minutes (assuming a 50% DoD), but rather for approximately 15 minutes.

On the other hand, lithium batteries can be discharged in 2 hours or at a 2C rate without causing any power loss. That means you can safely discharge a 50ah lithium battery at a 25 amps rate.

Note: look at your battery's data sheet for more accurate numbers.

Here’s an example of how discharge time affects the usable capacity of a 50ah lead acid battery.

Usable 50ah lead acid battery capacityHours of discharge
50ah20 hours
45ah10 hours
43.5ah8 hours
41ah6 hours
40ah5 hours
35ah3 hours
30ah2 hours
25ah1 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 age matters

Batteries have a limited number of charge and discharge cycles before their performance begins to degrade, which is referred to as their life cycle.

  • Lead acid — After about 500 cycles will lose about 20% of its charge-holding capacity
  • Lithium (LiFePO4) — After about 2000 cycles will lose about 20% of its charge-holding capacity

3. Ambient temperature

The efficiency of your battery decreases as the outside temperature increases. Typically, batteries function optimally when the temperature is between 68°F and 77°F (20°C to 25°C).

As a general rule, an increase in temperature to 77°F or 25°C can reduce battery performance by 50%.

How long will a 50ah battery last?

Here are tables showing the estimated backup time of a 50ah lead acid and lithium battery under various loads.

12v 50ah lead acid battery

AppliancePower consumption (Watts)Runtime (Lead Acid)
Fridge300 watts2 hrs
TV60 watts3.5 hrs
Trolling motor720 watts20 minutes
Ceiling Fan120 watts2 hrs
Computer300 watts40 minutes
LED Bulb20 watts11 hrs
How long will a 50ah lead acid battery last?

12v 50ah lithium (LiFePO4) battery

AppliancePower consumption (Watts)Runtime (Lithium)
Fridge300 watts5 hrs
TV60 watts8.5 hrs
Trolling motor720 watts40 minutes
Ceiling Fan120 watts4 hrs
Computer300 watts1.5 hrs
LED Bulb20 watts25 hrs
How long will a 50ah lithium (LiFePO4) battery last?

50ah battery: FAQs

What does 50Ah battery mean?

12v 50ah battery means you can draw 2.5 amp @ 12v (30 watts) for 50 hours.

How many watts is 50Ah battery

50ah battery is equal to 600 watts @ 12v, 1200 watts @ 24v, 2400 watts @ 48v

How long will a 50Ah battery last on an inverter?

50ah lead acid battery will last about an hour on an inverter running 230 watts of load.

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I hope this guide was helpful to you if you have any queries contact us. Thank You!

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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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