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10 Things you need to know about Lifepo4 Batteries

Table of Contents

What are LiFePO4 Batteries?

LiFePO4 batteries are a type of lithium battery built from lithium iron phosphate. Other batteries in the lithium category include:

  • Lithium Cobalt Oxide (LiCoO22)
  • Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2)
  • Lithium Titanate (LTO)
  • Lithium Manganese Oxide (LiMn2O4)
  • Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2)

LiFePO4 vs. Lithium Ion Batteries

Now that we know what LiFePO4 batteries are, let’s discuss what makes LiFePO4 better than lithium ion and other lithium batteries.

The LiFePO4 battery isn’t great for wearable devices like watches. Because they have a lower energy density compared to other lithium-ion batteries. That said, for things like solar energy systems, RVs, golf carts, bass boats, and electric motorcycles, it’s the best by far. Why?

Well, for one, the cycle life of a LiFePO4 battery is over 4x that of other lithium ion batteries.

It’s also the safest lithium battery type on the market, safer than lithiom ion and other battery types.

And last but not least, LiFePO4 batteries can not only reach 3,000-5,000 cycles or more… They can reach 100% depth of discharge (DOD). Why does that matter? Because that means, with LiFePO4 (unlike other batteries) you don’t have to worry about over discharging your battery.

A LiFePO4 Battery for Every Application

LiFePO4 technology has proven beneficial for a wide variety of applications. Here’s a few of them:

  • Fishing boats and kayaks: Less charging time and longer runtime means more time out on the water. Less weight allows for easy maneuvering and a speed boost during that high-stakes fishing competition.
  • Mopeds and mobility scooters: No dead weight to slow you down. Charge to less than full capacity for impromptu trips without damaging your battery.
  • Solar setups: Haul lightweight LiFePO4 batteries wherever life takes you (even if it’s up a mountain and far from the grid) and harness the power of the sun.
  • Commercial use: These batteries are the safest, toughest lithium batteries out there. So they’re great for industrial applications like floor machines, liftgates, and more.
  • Much more: In addition, lithium iron phosphate batteries power many other things. For example – flashlights, electronic cigarettes, radio equipment, emergency lighting and much more.

Is LiFePO4 better than lithium ion?

The LiFePO4 battery has the edge over lithium ion, both in terms of cycle life (it lasts 4-5x longer), and safety. This is a key advantage because lithium ion batteries can overheat and even catch fire, while LiFePO4 does not.

Is LiFePO4 more dangerous than AGM or lead acid?

Nope. It’s actually quite a bit safer. And for a number of reasons, including the fact that LiFePO4 batteries don’t leak toxic fumes. And they don’t spill sulfuric acid like many other batteries (like lead acid.) And like we mentioned earlier, they don’t overheat or catch fire.

What is the life expectancy of LiFePO4 batteries?

Life expectancy is one of the biggest perks, if not the biggest perk of LiFePO4. Our lithium batteries are rated to last around 5,000 cycles. That is, 10 years or so (and often more), depending on usage of course.

Even after those 5,000 cycles, our LiFePO4 batteries can still function at 70% capacity. And better still, you can discharge past 80% without a single issue. (Lead acid batteries tend to gas out when discharged past 50%.)

Here are lithium iron phosphate (LiFePO4) battery voltage charts showing state of charge based on voltage for 12V, 24V and 48V LiFePO4 batteries — as well as 3.2V LiFePO4 cells.

Note: The numbers in these charts are all based on the open circuit voltage (Voc) of a single battery at rest. If your LFP battery manual has its own discharge curve and charging parameters, they should take precedence over the ones below.

12V LiFePO4 Battery Voltage Chart

Voltage Capacity
14.6V 100% (charging)
13.6V 100% (resting)
13.4V 99%
13.3V 90%
13.2V 70%
13.1V 40%
13.0V 30%
12.9V 20%
12.8V 17%
12.5V 14%
12.0V 9%
10.0V 0%

Here’s a printable version of the above chart:

LiFePO4 Battery 12.8Voltage capacity
LiFePO4 Battery 12.8Voltage capacity

And here it is graphed out:

LiFePO4 Battery Voltage capacity
LiFePO4 Battery Voltage capacity

12V 100Ah LiFePO4 batteries are currently some of the most popular for off-grid solar power systems. They’re a drop-in replacement for 12V lead acid batteries, and a great upgrade.

They are fully charged at 14.6 volts and fully discharged at 10 volts. They are made by wiring four 3.2V LiFePO4 cells in series.

12v100ah lifepo4 battery
12v100ah lifepo4 battery

12V LiFePO4 Battery Charging Parameters

  • Charging voltage: 14.2-14.6V
  • Float voltage: 13.6V (or disabled)
  • Maximum voltage: 14.6V
  • Minimum voltage: 10V
  • Nominal voltage: 12V or 12.8V

24V LiFePO4 Battery Voltage Chart

Voltage Capacity
29.2V 100% (charging)
27.2V 100% (resting)
26.8V 99%
26.6V 90%
26.4V 70%
26.2V 40%
26.0V 30%
25.8V 20%
25.6V 17%
25.0V 14%
24.0V 9%
20.0V 0%

Here’s a printable version of the above chart:

LiFePO4 Battery 25.6Volt Capacity
LiFePO4 Battery 25.6Volt Capacity

And here it is graphed out:

LiFePO4 Battery 25.6V Capacity
LiFePO4 Battery 25.6V Capacity

24V lithium iron phosphate batteries are another popular option for DIY solar power projects. You can either buy a 24V LiFePO4 battery off the shelf, or get two identical 12V LiFePO4 batteries and connect them in series to make a 24V battery bank.

LFP24-100 24V100Ah LiFePO4 Lithium Battery
LFP24-100 24V100Ah LiFePO4 Lithium Battery

They are fully charged at 29.2 volts and fully discharged at 20 volts. They are made by connecting eight 3.2V LiFePO4 cells in series.

24V LiFePO4 Battery Charging Parameters

  • Charging voltage: 28.4-29.2V
  • Float voltage: 27.2V (or disabled)
  • Maximum voltage: 29.2V
  • Minimum voltage: 20V
  • Nominal voltage: 24V or 25.6V

48V LiFePO4 Battery Voltage Chart

Voltage Capacity
58.4V 100% (charging)
54.4V 100% (resting)
53.6V 99%
53.2V 90%
52.8V 70%
52.4V 40%
52.0V 30%
51.6V 20%
51.2V 17%
50.0V 14%
48.0V 9%
40.0V 0%

Here’s a printable version of the above chart:

LiFePO4 Battery 51.2V Capacity
LiFePO4 Battery 51.2V Capacity

And here it is graphed out:

LiFePO4 Battery 51.2Volt Capacity
LiFePO4 Battery 51.2Volt Capacity

48V batteries are more popular for larger solar systems. They rarely make sense for small-scale projects. Designing a higher voltage solar system allows you to keep amperage low, thereby saving you money on wiring and equipment costs.

48V LiFePO4 batteries are fully charged at 58.4 volts and fully discharged at 40 volts. They are made by connecting 16 3.2V LiFePO4 cells in series.

48V LiFePO4 Battery Charging Parameters

  • Charging voltage: 56.8-58.4V
  • Float voltage: 54.4V (or disabled)
  • Maximum voltage: 58.4V
  • Minimum voltage: 40V
  • Nominal voltage: 48V or 51.2V

3.2V LiFePO4 Cell Voltage Chart

Voltage Capacity
3.65V 100% (charging)
3.4V 100% (resting)
3.35V 99%
3.33V 90%
3.3V 70%
3.28V 40%
3.25V 30%
3.23V 20%
3.2V 17%
3.13V 14%
3.0V 9%
2.5V 0%

Here’s a printable version of the above chart:

LiFePO4 Battery 3.2V Capacity
LiFePO4 Battery 3.2V Capacity

And here it is graphed out:

LiFePO4 Battery 3.2Voltage Capacity
LiFePO4 Battery 3.2Voltage Capacity

Individual LiFePO4 cells have a nominal voltage of 3.2 volts. They are fully charged at 3.65 volts and fully discharged at 2.5 volts.

You can buy individual LiFePO4 battery cells online. They’re best used for making your own lithium batteries. You can wire cells in series and parallel to make LFP batteries with your desired voltage and capacity combinations.

3.2V LiFePO4 Cell Charging Parameters

  • Charging voltage: 3.55-3.65V
  • Float voltage: 3.4V (or disabled)
  • Maximum voltage: 3.65V
  • Minimum voltage: 2.5V
  • Nominal voltage: 3.2V

3 Ways to Check LiFePO4 Battery Capacity

1. Measure Battery Open Circuit Voltage with a Multimeter

Pros: Moderately accurate

Cons: Must disconnect all loads and chargers and let battery rest

A battery’s voltage changes depending on its charge and discharge rate. Plus, LiFePO4 batteries have a relatively flat discharge curve from around 99% to 20% capacity. Because of these factors, it can be hard to estimate their state of charge from voltage alone.

To get an even somewhat accurate estimate of LiFePO4 battery capacity based on voltage, you first need to disconnect any loads and chargers from the battery. (Don’t forget to disconnect your solar panels from your charge controller first!)

Let the battery rest for a little while — I usually wait 15-30 minutes — and then measure its open circuit voltage with a multimeter.

Compare your measurement to the right voltage curve above, or the state of charge chart in your battery manual. Use it to get a rough estimate of your battery’s remaining capacity.

For example, I own the Bravabattery 12V 150Ah LiFePO4 Deep Cycle Battery . I wanted to check its capacity after having stored it for a few weeks. I brought it out of storage and measured its voltage with a multimeter. I got 13.23 volts.

I then compared this number to the 12V LiFePO4 state of charge chart above, as well as the one in the battery manual.

Based on the charts, I’d estimate my battery’s state of charge was somewhere around 80%.

I like this method best for estimating the state of charge of an LFP battery I’ve just received or just pulled out of storage. The battery is already at rest and not connected to anything. I find it too inconvenient to disconnect everything once the battery is in use.

2. Use a Battery Monitor

Pros: Most accurate, convenient

Cons: Good battery monitors are expensive

The best way to track battery capacity is to connect a good battery monitor — such as the Victron SmartShunt or Victron BMV-712.

Battery monitors track the amount of amp hours consumed to accurately estimate the state of charge. They also display useful system specs such as battery voltage and current. Some connect via Bluetooth to your phone so you can check your LiFePO4 battery’s capacity in a mobile app.

 

3. Use a Solar Charge Controller

 

Pros: Convenient

Cons: Inaccurate

If you charge your LiFePO4 battery with solar panels, you may be thinking:

“My solar charge controller already measures battery voltage. I can just use it to check battery capacity.”

But!

This voltage reading is largely inaccurate. It suffers from all of the problems mentioned above, plus it’s done while the battery is connected to loads and chargers.

(Not to mention that some charge controllers have incorrect voltage readings.)

For example, recall that when I checked my battery’s voltage with a multimeter at the battery terminals, I got a voltage reading of 13.23 volts. That correlates to a roughly 80% state of charge.

But when I connected my battery to an MPPT charge controller, the controller measured 13.0 volts. That correlates to a roughly 30% state of charge — a difference of 50%! Granted, some charge controllers have much more accurate battery voltage readings than others.

After all, voltage drops under load. And a charge controller is a load. If I were to connect a solar panel and start solar charging the battery, its voltage would quickly jump.

Checking battery capacity this way is convenient. But beware that it can be quite inaccurate. I generally use this voltage reading just to make sure my battery isn’t close to being fully discharged.

If you use this method and want to make sure it’s as accurate as possible, you can buy a battery voltage sensor.  A voltage sensor gives the controller a more accurate voltage reading, especially in solar power systems with long wire runs.

LiFePO4 Voltage FAQ

What is the voltage of a fully charged 12V LiFePO4 battery?

A fully charged 12V LiFePO4 battery will have a charging voltage of around 14.6 volts and a resting voltage of around 13.6 volts.

What is the charging voltage of a 12V LiFePO4 battery?

The charging voltage for 12V LiFePO4 batteries is 14.2 to 14.6 volts. This works out to a charging voltage of 3.55 to 3.65 volts per cell.

Most often, you’ll see LiFePO4 battery chargers and solar charge controllers use a charging voltage of 14.4 volts for 12V lithium batteries.

What is the minimum voltage of a 12V LiFePO4 battery?

The minimum voltage of many 12V LiFePO4 batteries is around 10 volts. The battery’s BMS should detect when the battery voltage falls to around 10 volts and trigger low-voltage cutoff. (Low-voltage cutoff is also called low-voltage disconnect, which you’ll sometimes see abbreviated LVD.)

Note: Some batteries have higher cutoff voltages, such as 10.6V. So the limit in your battery manual may not be exactly 10V.

LiFePO4 batteries in low-voltage cutoff enter a sleep mode to protect the battery cells from over discharge. LFP batteries in sleep mode can have very low voltage readings, usually less than 5 volts. You may think that the battery is dead, but really it’s just sleeping.

Once a battery enters sleep mode, it needs to be woken up. Refer to your battery manual for instructions on how to do this. If your manual doesn’t have instructions, check out our tutorial on how to wake up a sleeping LiFePO4 battery.

What is the float voltage of a 12V LiFePO4 battery?

LiFePO4 batteries don’t need to be float charged because they don’t leak charge the way lead acid batteries do.

If you can, disable float charging on your charge controller or battery charger. If you can’t, prevent the battery from entering float charge by setting the float voltage to that recommended in the battery manual — usually 13.6 volts ± 0.2 volts.

How much can you discharge a LiFePO4 battery?

Many LiFePO4 batteries can discharge 100% of their rated capacity every time with no ill effects.

However, many manufacturers recommend discharging only 80% to maximize battery life. In fact, some brands state the cycle life of their batteries based on 80% depth of discharge (DoD).

For comparison, lead acid batteries can only discharge 50% of their rated capacity. So a 12V 150Ah LFP battery has as much usable capacity as a 12V 200Ah lead acid battery.

Slim Lifepo4 battery with BT
Slim Lifepo4 battery with BT

 

 

 

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