How Long Will a 200Ah LiFePO4 Battery Last

Are you considering changing your old lead-acid batteries for something more modern? Or are you looking to add capacity to your battery bank without requiring extra space? If so, you may have heard about Lithium batteries and more specifically Lithium-ion batteries.  

Lithium-ion batteries offer a number of advantages over lead-acid batteries. They offer a much longer life up to 10 times. They are much lighter and you can actually get the same capacity of lithium-ion batteries at a quarter the weight of your lead-acid batteries. They are also much more compact and will take up less space.

Because you can use up to 90% of a LiFePO4 battery’s capacity, a 200 Ah LiFePO4 battery can provide almost twice the capacity of an AGM battery that can only be discharged up to 50% of its capacity. You can also charge a lithium-ion battery faster meaning you get a more usable capacity from the batteries.

Lithium-ion batteries are also much more efficient and will charge and discharge much more quickly. This makes them a great option for off-grid living.

How Much Power Can You Pull from a 200Ah LiFePO4 Battery?

Most batteries however are indicated in Amp-hours. Amp-hours is a unit of electrical charge. It is the amount of charge that is delivered by a battery in one hour.

Power is indicated in Watts and Energy is indicated in Watt-Hours.

1 Watt-hour is the amount of energy that is used by a 1-watt appliance over the course of 1 hour. It can also be thought of as the amount of energy that is stored in a 1 watt-hour battery.

Watt-hours can tell you how long a battery can run an appliance. For example, to run a 200 Watt refrigerator for 8 hours you will need 1600 Watt-Hours.

To convert Amp-hours to Watt-hours you simply multiply the amp-hours by the voltage of the system. So a 200 Ah battery will provide:

200 x 12 = 2400 Watt-hours.

That’s 2.4 Kwh

How Many Hours of Back up from a 200 Ah Battery

You can also work from the requirements of your appliances to see whether a 200 Ah battery can provide enough power:

To understand your energy requirements you need to convert them to Watt-hours. To calculate Watt-Hours you simply take the wattage of an appliance and multiply it by the time you use the device. 

 

ApplianceWattageUsage (Hours)Daily Watt-Hour Requirements
Refrigerator20081600
LED Lights205  100
Mini Fan40  320
Laptop605300

 

The total comes to around 2320 watt-hours. 

This is less than the 2400 Watt-hours that is available in the battery. However, as we have said we can only discharge up to 90% of the capacity. There will also be system losses due to converting the DC power to AC power and also through the loss through the wiring.  So it will be better to reduce the power requirements of your devices.

How Many Amps to Charge a 200Ah LiFePO4 Battery

There are exceptions though; if you are using solar panels to recharge the battery you can actually end up getting a higher capacity from the battery and running even more appliances.

How Many Solar Panels to Charge a 200Ah LiFePO4 Battery

A lithium battery can be charged using 100% of its capacity meaning that you can actually use 200 amps to charge a 200 ah battery in one hour. However, this is not recommended and more likely use 50% or 0.5C to charge the battery n two to three hours. This will vary with manufacturers.

So with a 200 ah lithium-ion battery, you charge it in 2 hours with 100 amps and four hours with 50 amps. So to get the solar panel size you multiply the voltage by the amperage. A 12v solar panel will have an 18v voltage for potential voltage, therefore;

18 x 50 = 900 watts

You can use a 1000-watt solar panel or two 500-watt solar panels in parallel to charge the battery in four hours. 

Because a lithium battery can also be discharged up to 90% of its capacity this means that you can use your high wattage appliances early in the morning and afternoon and a solar panel can fully recharge the battery in a few hours. 

Other Downsides to Lithium-ion batteries 

Some batteries claim to be drop-in replacements for Lead-acid batteries for your systems. But this may not be accurate. Offgrid batteries and systems work on a 12v system which you will get on Lithium batteries.

Lithium cells have a rating of 3.7v and four cells will come to around 14V which can work in a 12v system. Also, the size of the battery may be the same or even smaller and fit right into where the old batteries were. 

But this does not mean that you can just buy the batteries and fit them right in and expect everything to be running smoothly. Replacing lead acid with lithium-ion batteries is not an easy undertaking. You may need to change some of your electrical system components for this to happen

What Does a Deep cycle battery mean? 

Deep cycle batteries are the backbone of the solar power industry for a reason: they can store a lot of charge. Because they are designed to be discharged and charged over long periods, they are ideal for use in solar panels and renewable energy storage. They can also be used in campers and boats where you need to store power to use off-grid. 

A deep cycle battery is a battery designed to be regularly discharged and recharged. Unlike a starter battery, a deep cycle battery is designed to withstand repeated deep discharge cycles. A deep cycle battery is typically used in applications where sustained discharge over long periods of time is required, such as in electric golf carts, marine applications, and forklifts. 

Deep cycle Battery

How far to discharge a deep cycle battery 

A deep cycle battery can be discharged up to 90% however for lead-acid batteries it is recommended to only discharge them up to 50%. This ensures that the battery last longer. This is one of the biggest differences between lithium and lead-acid deep cycle batteries. 

However, the amount of charge that a battery can provide depends on its C rating. Amp-hour is the rating used to rate how much amperage a battery can provide for exactly one hour.

Deep cycle batteries will have info on the Ah rating at multiple C ratings. A battery’s C rating is the maximum amount of current that a battery can safely provide. The rating is given in amps and is typically abbreviated as “C.”  

Batteries will be imprinted with numbers like 0.1C, 0.2C, 1C, C10, and so forth. These indicate the C rating of the battery. “C” rating is used as battery power can not be discharged all at once the time is a factor when discharging batteries to ensure safe use. 

For example, 12V100Ah battery, C is 100. “1C discharge” means 100A as discharge current. And just like that, 0.1C is 10A, 0.5C is 50A, which equals the number before C multiplied by the C value.

Deep cycle batteries are usually rated at 0.2C and are meant to be discharged over a 20hr period. 

A lithium-ion battery can last up to 6 months when not and will only discharge partially. This is because they have a low discharge rate. This is compared to lead-acid batteries that will not go beyond 30 days and you have to use a battery maintainer to keep the battery alive. 

Lifespan 

A  lithium-ion battery and specifically a LiFeP04 battery should last more than 10 times longer compared to other types of rechargeable batteries under normal use conditions.

LiFePO4 battery cells also have a longer life cycle, up to 5000 cycles while the lead-acid batteries are typically around 300–500 cycles

 

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