LiPo Batteries for Drones (Everything You Need to Know)


What battery does your drone use? It’s most likely a LiPo battery. These batteries are most commonly used in toys, drones, RCs, and even model airplanes and trains. Why is this type of battery the most common choice?

Lipo batteries are the best thing that ever happened to the drone community and other toy and hobby communities because of their smaller size and larger capacities. These qualities are essential for longer flight times. However, they pose a potential fire hazard if not handled properly.

It’s important to know the ins and outs of your drone batteries to get the most out of them, so I’m going to discuss everything you need to know about LiPo batteries, including how to safely store them and dispose of them off if they get damaged.

What is a LiPo battery?

LiPo stands for Lithium Polymer or Lithium-ion polymer, which are rechargeable batteries made of polymer electrolytes. In simple terms, instead of using a liquid form of electrolyte, LiPo batteries use polymer, which is more of a “sheet” that stores a charge and transmits power to the device when necessary. 

LiPo batteries have a soft shell casing, unlike ion batteries that have a hard shell. The polymer and the ability to enclose it in a soft cover make these batteries suitable for RCs since you can form them into different shapes, unlike with hard shells.

Now let’s look at some of the main concepts that make up a LiPo battery. I will be referring to the image below throughout the article.

Image credit: Ingolov.com

Voltage (Nominal Voltage)

Nominal voltage is the “named” voltage, or the voltage of a battery when at rest. It should not be confused with the rated voltage or operating voltage. For instance, the nominal voltage of most LiPo batteries is 3.7 V, but when fully charged, LiPo batteries have a 4.2 voltage. And when you’ve discharged them to the minimum, they should have a 3.0 Voltage.

This brings us to the labeling. You will find most batteries labeled as 2S, 3S, 4S, or 6S. These numbers refer to the number of cells of the batteries arranged in a series form. So, the S stands for Series. 

You’ll notice that there’s also a number denoted by C on the battery. In the image above, we have 50C. But that doesn’t mean “Cells.” It means Discharge Rating, which I will discuss in a minute.

To get the total voltage, you add the voltage of each cell. For instance, a 2S battery has two cells, so the total voltage will be 7.4V, 3S batteries like the image above will have 11.1 V, 4S batteries will have 14.8, etc…

You may come across older batteries labeled as 2S2P, which means there are four cells; 2 in Series arrangement and 2 in Parallel structure. But such batteries have been phased out and replaced by the newer models.

So, what is the importance of knowing the voltage? It translates to how fast a motor can rotate, which then translates to the power and speed of a drone. You may have come across quadcopters with motors labeled as kV. At first, I thought, and some users did too, that kV stands for kilovolts. Well, that’s not the case. 

kV actually stands for RPM (rotations per minute) for every volt. So, if the quadcopter has a 3000 kV, you’ll have to multiply that by the battery’s voltage. For instance, a 2S battery will produce 22,200 RPM. The more voltage the battery has, the faster the motors rotate and the more power the drone will have.

Capacity

To understand capacity, let’s use the common water tank analogy. The voltage I just described is the pressure of the tank. Simply put, the more pressure/force a tank has, the more powerfully it will eject the water. Now, the capacity will be the amount of water the tank can hold at a time. So, when speaking of batteries, it means the amount of charge it can hold, which translates to how long the battery can last. 

The capacity of a battery is measured in milliamp-hours (mAh). Our battery above has 5200mAh, but you’ll find some batteries with capacity as high as 12,000mAh, and some with less than 5000mAh. Also, 1000mAh, make 1Ah (Amp-hours).

While a battery with more capacity seems like a good idea since you get to use a drone for longer, you also need to consider the effects on the overall system of the drone. 

For one thing, more capacity means more weight, and most drones can’t function as well when they’re too heavy. Secondly, if the motors run for too long without cooling down, they may catch fire and even damage the entire drone.

Discharge Rating (C)

Also known as the “C” Rating, the discharge rating is the amount of charge/load you can continuously drain from the battery without damaging it. If you use a device that draws more charge at a time, you could damage the battery. 

Now, our battery has a discharge rating of 50C, which means you’re going to multiply 50 by the battery’s capacity in Amps.

So, our battery’s capacity is 5200mAh. In amps, that is 5.2Ah.

50*5.2 = 260 A.

So, you can continuously draw 260 A from this battery. Now that’s the continuous rating. 

There’s also a Burst Rating, which is the highest amount of charge you can draw within 10-second bursts. Our battery above has a burst rate of 100C, which means it can survive 520A blasts occasionally. This could be during the acceleration of a drone, and it will most often be more than the continuous rating.

When buying extra batteries, make sure you’re aware of the power draw the drone needs and what you’ll be using the drone for. Racing drones may need batteries with a higher discharge rating.

Internal Resistance

While the internal resistance is not part of the battery design, it’s essential to mention it. Using the water tank analogy, we can best explain resistance with a hose. A hose is supposed to allow water to flow smoothly. But if there’s a kink in the hose, it limits how well the water flows—the bigger or deeper the kink, the more insufficient the water flow. 

The same case applies to LiPo batteries and any other electronics. The higher the resistance, the less the charge that reaches the critical components of the drone. The reason they can’t indicate the resistance is that it builds up over time. 

The more you use the battery, a residue known as Li2O (lithium oxide) is deposited, adding to the internal resistance to a point where the battery becomes unusable. When the energy can’t get to the required components, it’s converted to heat. Heat then leads to more oxygen accumulation within the batteries and more lithium oxide build-up, which causes them to swell. The moment you see the battery swelling, you should stop using it. 

Using a swollen battery generates even more heat, and a process known as Thermal Runaway takes place. Eventually, the lithium oxide build-up, oxygen, heat, and humidity combine and explode into a fire.

The standard measurement for resistance is ohms (Ω). 

1 milliohms (mΩ) = 1 ohm.

It’s vital to keep checking your batteries’ resistance levels to make sure they are still usable. Most advanced chargers can help you measure the internal resistance either for one cell individually or for all cells together. 

Generally speaking, it’s safe to use a battery with a resistance ranging from 0 to 12 ohms. Anything more than that means you should consider replacing the batteries.

Why do drones use LiPo batteries?

LiPo batteries have many benefits for the drone industry since they are small and can carry a lot of charge in one cell (3.7 V to 4.2V). This makes it possible to build a large-capacity or high voltage battery for various applications without making the drone too heavy.

How to charge a LiPo battery?

LiPo batteries are pretty sensitive. You can’t use just any charger with them. Overcharging them could lead to damage or even a fire. Unlike other batteries, LiPo batteries use a CC/CV system which means Constant Charge/ Constant Voltage. 

As mentioned earlier, they can hold a maximum of 4.2 V. So, when the battery has 4.2 V on each charge, it maintains that voltage rather than continuously throwing current pulses.

The Charger

LiPo batteries use what are known as balancing chargers. These are charges that make sure each cell in the battery gets enough charge. Balancing chargers or chargers with inbuilt balancing can be pretty expensive, but they are worth it if you want your battery to last longer. Besides, a battery with an unbalanced charge (some cells with more charge) increases the risk of damaging the battery or even causing a fire.

The Current

Another aspect to consider when charging a LiPo battery is the amount of current. Fast chargers are the norm in some devices, where they send high amounts of current (amperes), charging a large battery within a short time. You can’t do that with a LiPo battery. LiPo batteries come with a rate at which you can charge them, just like the discharge rate.

Now, our battery above has a 2C charge rate. Like we calculated the discharge rate, you multiply the charging rate by the capacity. In this case, our battery has a capacity of 5.2Ah or (5200mAh).

5.2*2 = 10.4 A.

So, you should always charge this battery at 10.4 Amperes. Always check your battery to identify the suitable charge rate. You can charge with a lower rate, such as a 1C rate, but never go above what the labeling on the battery advises.

The Connectors

And lastly, you should make sure the charger you’re using has a connector compatible with those on your battery. As you can see in our battery above, each Lipo battery has two connectors. The yellow one goes (mostly XT-60) to the drone, while the white plugs go to the balancing charger. Most importantly, since you’re dealing with high voltage and amperage, the wires should be thick. 

How many LiPo batteries do you need for your drone?

Two to three batteries would be great for your drone. While it’s possible to have more batteries and fly for long, you risk damaging your rotors, especially when you run them for too long without allowing them to cool down. 

How to store LiPo battery

A LiPo battery should never be stored when fully charged. Neither should it be stored when below 3.0 V. Doing this could damage them completely. For instance, if you store them at full charge, the batteries will automatically discharge themselves, and they could end up with a voltage of less than 3 V.

The optimum storage voltage is 3.8 V. Always check the batteries’ voltage before storage. Thankfully most advanced chargers allow you to check the voltage, so charge them if they are below 3.0 V, and discharge them if the voltage is more than 3.8 V. 

Also, to prevent fires when in storage, always store LiPo batteries in fire-resistant bags such as the one pictured below.

Other storage areas such as ammo bags or firearm safes will still work as long as they are fireproof.

How to travel with LiPo batteries

If you’re planning to take your drone with you when traveling, you can safely bring 2 to 3 LiPo batteries. However, LiPo batteries are not allowed in the cargo cabin since they are a fire hazard. You will have to carry them with your other carry-on luggage. 

Before packing the batteries, make sure they are not damaged. You can place the batteries in a fireproof bag or a drone-carrying box with compartments for the batteries. Also, make sure you check the airline’s guidelines on carrying drones and batteries.

» MORE: If you’re planning to travel with your drone (and batteries!) read our Ultimate Guide to Traveling with a Drone for more tips on how to pack and fly with your gear. 

How long do LiPo batteries last?

LiPo batteries are designed to last at least 300 to 500 cycles when everything is perfect. That is, store them in the correct voltage, store them at the right temperature, avoid excess humidity, avoid puncturing them and charge them using the correct charger. 

However, it’s not always possible to maintain all of these conditions. That’s why most LiPo batteries average between 150 and 250 cycles. That can be anywhere between 1 year and 3 years, depending on how often you use your drone.

How to dispose of a LiPo battery

At one point, you will need to throw away your LiPo battery, which you should do very carefully. Here’s why.  As mentioned earlier, the Lithium oxide and oxygen build-up cause the battery to swell. And I mentioned, continued use could damage the batteries and cause a fire. 

However, even though you’re not using the battery, it could still cause a fire if you puncture it. The Thermal Runaway process could still occur, especially if the battery is still charged.

NOTE: Some companies offer warranties on the batteries. So, check that before trying any of the processes below.

Whether your batteries are dead or swollen, do the following before disposing of your LiPo batteries:

Start by checking the voltage. The ideal voltage for disposing of your battery should be 0.0 V. If it has some charge, discharge it with either of the following steps.

Make sure they are completely discharged before disposing of them. There are several ways you can do this. 

  1. You can use your balancing charger to discharge them or use them in the drone until they’re left with no charge. The latter process is risky since you could set your drone on fire.
  2. Another way to discharge it is using a salt water bath. Add warm water to a tray and saturate it with salt until no more salt can dissolve. Then soak the batteries in the salty water. 
  3. You can also drain it by connecting it to an LED light while the battery is dipped in sand. When the LED dims or goes off due to low voltage, disconnect it, and connect the positive and negative wires of the battery to cause a short circuit.

Once you’re sure it has no charge, you can throw it in your regular trash can or look for local battery disposal services.

Safety Precautions

Below are some safety precautions and a summary of how to extend a LiPo battery’s lifespan.

  • Always have a fire extinguisher nearby. LiPo batteries don’t do well in high temperatures and will often result in a fire. While a fire extinguisher is not the best for chemical reactions such as the one in LiPo batteries, it will help contain it.
  • Constantly monitor your batteries closely as they charge. It only takes a few seconds of the wrong temperatures for these batteries to explode. So, if you leave them and go to the store, or for a run around the neighborhood, you may come back to find your entire house on fire.
  • Make sure the storage area is at room temperature. I will stress again, LiPo batteries and high temperatures are sworn enemies.
  • Always store the batteries in a dry area, and make sure they don’t contact water since water facilitates the chemical reactions that cause a fire.
  • Always keep your batteries clean. Using a soft-bristled brush, clean the drone, the connectors, and the drone’s battery compartment.
  • Always keep the voltage between 3.0 V and 4.2 V, and store them at 3.7V.
  • Use a high-quality balancing charger.
  • Avoid using metallic objects that may connect the positive and negative, causing a short circuit. This could be when using pliers during the soldering process.

Conclusion

And there you have it. Hopefully, I’ve covered everything you need to know about LiPo batteries for drones. While they offer more benefits than other battery types, you need to handle them carefully to prevent potential hazards. 

As we’ve established, maintain them at the appropriate voltage, use the proper charger, avoid too hot or too cold temperatures, avoid using swollen batteries, never leave them unattended, and make sure the batteries are discharged before disposing of them. 

While you should take the risks seriously, these batteries are not something to scare you off though. Handled properly, you should never have to face an emergency. And don’t forget to have fun when flying your drones.

Elizabeth Ciobanu

Editor-in-Chief. Elizabeth is a full-time (homeschooling!) mom of four, and serial entrepreneur in a variety of enterprises, one of which is producing content for Droneblog. If free time existed, she would love to spend more time on hobbies such as flying a drone.

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