LifePO4 or lithium iron phosphate is a rechargeable battery known for having a long life cycle, high energy density, and for being safe to use compared to other lithium-ion batteries. They are commonly used to run solar electricity systems.
They are less prone to thermal runaway unlike their other counterparts, which means it is less likely to catch fire or explore due to overheating. This is because they require lower voltage and have stable cathode material. And, if they do overheat, they automatically turn off to cool down and conserve energy.
They don’t require being fully charged when in use and aren’t high maintenance.
On that note, in this article, we’ll tackle how to expand home power backup’s battery lifespan by taking a closer look at the LifePO4 voltage, SOC (state of charge) chart, etc.
What is the State of Charge or SOC?
According to TechTarget, the stage of charge (SOC) is a measurement of the amount of energy available in a battery at any specific point in time expressed as a percentage. Or in layman’s terms, SOC meant how much power a battery has before it needs to charge or be replaced. I.E. How much battery is left on your phone or laptop before the need to plug it in arises.
How to Measure the State of Charge?
There are different ways to determine the battery’s state of charge. They are the following:
- Voltage – is simple yet may provide inaccurate results because cell materials and temperature may affect the voltage. But in its simplest form, the higher the voltage is, the fuller the batter is. To ensure that you get an accurate reading, put the battery at rest for at least four hours before measuring it. Meanwhile, manufacturers recommend at least 24 hours of rest.
- Specific Gravity – requires a hydrometer to measure the SOC. It works by monitoring the density of liquid based on buoyancy. This means looking at any changes in the weight of the battery’s active chemicals while discharging. One of those chemicals is sulfuric acid. This active electrolyte decreases when the battery is used, resulting in the battery’s specific gravity diminishing.
- Counting Coulombs – works by measuring the current that’s flowing in and out of the battery. It uses Ampere-second (As) as the unit of measurement for charging and discharging.
The LifePO4’s Voltage
As stated above, new batteries come with a 30% charge in them. This is done by manufacturers to decrease the potential energy that can be released when shipping them. This amount is roughly about 13V.
And, like any type of battery, LifePO4 batteries have a specific discharge curve. Their voltage decreases as their capacity lessens from 100% to 0%. Provided below is a chart of the state of charge for four lithium voltage charts:
Click image to zoom/download chart
This chart only shows the voltage level of the battery and its equivalent capacity in percentage. But if you want to really see the charging state of the battery, you may want to get a multimeter or voltmeter. This will help you get the real-time current voltage and check the chart to see the corresponding number.
So, if you get a 24V LifePO4 battery that shows 26.1V on the voltmeter, the chart indicates that it’s about 60% on the SOC chart.
Factors that affect the battery’s SOC
There are a number of factors in the performance of the battery that may affect its SOC. Some of them include:
- Battery’s maintenance – how the battery is kept and maintained is important as the rest of the factors that affect its performance will follow. Proper maintenance includes working at a suitable temperature, using the right charger, and avoiding high current discharge.
- Battery temperature – like any of its counterparts, this battery’s performance is also affected by extreme heat. While it has its own safety measures to avoid overheating, there are external factors that may contribute to its malfunction.
- Battery chemistry – since LifePO4 is made out of different materials, its SOC will be different from lead-acid batteries
- Battery application – how or what the battery is used for greatly affects how fast or slow energy is being used off of its system.
How to Properly Charge Your Battery as per SOC
Properly charging the LifePO4 is part of its maintenance. Done right, the battery’s quality and performance will be maintained and prolonged.
Each kind of battery has its own suggested level of voltage that must be reached in order to get maximum performance while keeping the battery health good. You may use the SOC chart as a guide when recharging your batteries. For example, the 80% charge for a 24v battery is 26.6v.
What is Depth of Discharge (DOD) and what makes it different?
Another point of discussion when it comes to extending one’s battery life is DOD of Depth of Discharge, which is about the discharged capacity of the battery in relation to its overall capacity. In layman’s terms, the more often a battery is used (charged and recharged) the shorter its lifespan going to be.
For best practice, it isn’t recommended to completely discharge the battery as this will increase the battery’s wear and tear.
Manufacturers have a recommended maximum DOD to ensure optimal performance and prolonged battery life. So, be sure to check the battery’s manuals for such information.
Maintenance and knowledge are the keys to ensuring that our home power backup’s battery is working at its best.
Use the provided information to significantly affect the lifespan and energy storage of the battery.
Be sure to always be on top of the battery’s voltage and be sure that it's within the suggested range for continued high-quality usage.
* We want to give credit where credit is due. Professional writer, Cris Ilao, contributed research and content to this blog titled: LiFePo4 Voltage Chart Thank you, Cris, for your contributions!