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

12v 50ah Lithium battery with a 50% DoD limit will last between 20 hours (running a 25-watt AC appliance) to 1 hour (running a 540-watt AC appliance).

In this post, you’ll learn how long will a 50ah battery last running a different size AC or DC load (with examples).

Also, I’ll share the manual calculation method and some other important points to keep in mind that the other websites aren’t talking about.

Need an easy solution? use our battery runtime calculator ( given below ) and Enter the battery specs and the total load in watts to find out how long will a 50ah battery last

Battery Runtime Calculator

Battery Capacity
Ah
Battery Volts
V
Select Battery Type
Load Connected with inverter?
Total Load (watts)
Wh

Note! use my solar panel size calculator to find out what size solar panel you need to recharge your battery in desired hours with solar panels.

Assumptions:

  • Inverter Efficiency: 90%
  • Lead-acid battery: 50% depth of discharge limit
  • Lithium (LiFePO4): 100% depth of discharge limit

Battery Depth of discharge DoD: is the percentage of the battery that has been discharged relative to the total battery capacity. The recommended depth of discharge limit for lead-acid, AGM, and gel batteries is about 50%. Only lithium (LiFePO4) batteries can be fully discharged to 100%.

How To Use The Calculator

  • Enter the battery capacity in amp-hours (Ah): in this case, it’ll be 50
  • Enter the battery voltage: is this a 12, 24, or 48-volt battery?
  • Select the battery type:  Select “Lead-acid” if you’re using a flooded or sealed (AGM or gel) lead acid battery. Select “Lithium (LiFePO4)” if you use a lithium-iron-phosphate battery.
  • load Connected with inverter?: Are you using an inverter to run the load or is the load connected directly through the battery?
  • Enter total load in watts: Enter the total load in watts (e.g 500 for 500 watts of output load)

After entering the information, click “Calculate” button to find out how long the battery last running a load.

if you’ve got some time keep reading… I’ll share a manual calculation method that you can use in the future to calculate any size battery runtime on any load and also some additional information about batteries that will affect the battery last time.

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

how long will a 50ah leisure battery last?

12v 50ah leisure battery with 50% DoD limit last about an hour running a 270 watts of AC load.

Video – All about battery basics (Must watch!)

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

Steps to calculate 50ah battery runtime

Follow these steps to calculate the battery life/runtime while running a load.

Steps

1- Converter battery ah into watt-hours (Wh). to calculate the battery capacity in watt-hours use this formula

Battery capacity in watt-hours = Battery amp-hours (Ah) * Battery Volts 

let’s say you have a 12v 50ah battery

50ah battery in watts = 50 * 12 = 600 watt-hours 

2- Multiply the battery watt-hours by the battery depth of discharge limit. ( Default battery depth of discharge limit, Lead-acid battery: 50% DoD limit; Lithium: 100% DoD limit ). Let’s say you have a lead-acid type battery

Battery capacity in wh after DoD limit = 600 * 50% = 300wh

3- Multiply the battery capacity after the DoD limit with the inverter efficiency rate to calculate the AC watt-hours ( Most of the inverters are about 90% efficient)

Battery AC watts = 300 * 90% = 270 AC watt-hours 

4- Divide the battery AC watt-hours by the total load connected. Let’s say a 100-watt appliance is connected to your 50ah battery

50ah battery runtime on 100w appliance = 270 / 100 = 2.7 hours

How long will a 50ah battery last? – chart

ApplianceWattage consumptionHow long will a 50ah battery last
Fridge300 watts55 minutes
TV60 watts4.5 hours
Trolling motor720 watts22 minutes
Ceiling Fan120 watts2.2 hours
Computer300 watts55 minutes
LED Bulb20 watts13.5 hours
Dishwasher1800 watts10 minutes
Toasters1200 watts13 minutes
How long will a 50ah battery last?

Summary

  • 12v 50ah Lead-acid battery with a 50% DoD limit will last about 22 minutes on a trolling motor.
  • 12v 50ah Lithium battery with a 100% DoD limit will last about 44 minutes on a trolling motor.
  • 12v 50ah lead-acid battery with a 50% DoD limit will run a fridge/refrigerator for about 55 minutes

Note! The values are based on AC output load with a 90% efficient inverter.

Assumptions & Shortcomings of All These Methods

Here are some extra yet important points to keep in mind when figuring out how long will your 50ah battery will last running a load

Battery life cycle count:

  • The storage capacity of the battery will decrease with every cycle ( a cycle is when you charge and discharge the battery to its DoD limit ).
  • 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 )

Batteries are rated for 5 amps over 20 hours of time:

  • Especially lead-acid type batteries are designed to be discharged at 20 hours. ( means 50ah lead-acid batteries are recommended to be discharged @ 2.5 amps in order to maintain the battery health and reduce the discharge efficiency ).
  • on the other hand, AGM and lithium (LiFePO4) can be discharged at 50% of their capacity.
  • Discharging your battery at a higher rate will increase heat in the battery’s internal cells which will cause power loss. (this factor isn’t included in my above-given methods).
  • For example, if you discharge your lead-acid battery with 50 amps then it’s will not last 15 minutes ( keep in mind the 50% DoD limit ). but it may last about 5-10 minutes.
  • Check the battery discharge rate on the specs sheet of your battery or it’ll be mentioned on the battery (1h → 1C, 2h → 0.5C, 5h → 0.2C, etc.)

Related FAQ’s

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 battery with a 50% DoD limit last about an hour on an inverter running 540 watts of load.

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

I'm an experienced Sales Consultant with a demonstrated history of working in the renewables and environment industry. Skilled in Photography, Customer Service, and Sales.