Drone battery safety is a fundamental aspect of the hobby. A standard four cell lithium polymer (LiPo) 1500mAh battery at full charge stores a massive 25Wh (watt hours) of energy. When damaged or incorrectly charged, these batteries can go up in flames. In this article, I will discuss drone battery safety and how to safely store & charge LiPo batteries.
A Quick Disclaimer
All information in this article should only be considered as general advice. Drone battery safety is your responsibility and you should use the information in this article at your own risk.
Why You Should Care About Drone Battery Safety
It is essential not to overlook drone battery safety. Many pilots’ houses have burnt down as a result of incorrect drone battery safety precautions. I would go as far as to say that everyone who has been flying in this hobby for a few years will know at least one person who had their house burn down or had a close call as a result of a LiPo battery malfunction. Nurk FPV’s video below demonstrates what happens when a lithium battery fails.
It is safe to say that nobody would like that to happen inside their house or at the field. By implementing drone battery safety measures into your LiPo charging and storage, damage as a result of a battery or charger malfunction will be minimised.
Why Does a LiPo Battery Fail
Before I move on to drone battery safety precautions, it is important to first understand what is happening when a LiPo battery fails. The three main battery failure modes are overcharging, over discharging and cell damage.
When a LiPo battery is overcharged, the anode of the battery becomes plated with lithium metal and the cathode produces carbon dioxide. The pressure inside the battery rises as more gas is produced until the outer skin of the LiPo bursts and vents gas. LiPo venting is usually accompanied by flames which leads to the entire battery destroying itself. Overcharging can be prevented by charging LiPo batteries to a maximum of 4.2 volts per cell (or 4.35V for lithium high voltage packs) and charging at a safe current setting. I recommend a 1C charge rate. To learn more about C ratings, you can read this article here.
When quickly discharged in situations such as a drone race, a LiPo battery will heat up. If excess current is drawn from the battery causing it to overheat, gasses will form inside the battery. Like overcharging, if enough gas forms and the LiPo bursts, it will commonly vent with flames. If a LiPo is discharged below its stated C-rating, there should not usually be a safety issue (unless, as happens occasionally, LiPo manufacturers lie about the C-rating of their batteries). The image below shows a ‘puffed’ LiPo after it was over discharged in a race. Fortunately, not enough gas was produced to burst the battery.
Individual layers of a LiPo cell are separated with a thin plastic film. If this film is punctured and the batteries’ anodes and cathodes short out, this will also cause the battery to enter a thermal runaway state. Smartphone battery developers have spent billions after the Galaxy Note 7 incident to minimise battery failures as a result of damage. Although a hard impact can force a LiPo to fail, battery fires rarely occur at race events. Despite this, pilots and event organisers make sure to employ safety precautions to ensure a high level of drone battery safety.
There a multitude of safety precautions you can take to ensure drone battery safety. Listed below are the most important precautions.
When charging your batteries, it is highly important to charge them in an area clear of flammable items and materials. Common charging locations include garages/sheds with concrete floors and unused fireplaces. It is also a wise drone battery safety precaution to charge any batteries away from high value items such as cars, tools or drone equipment. My charging location of choice is on the concrete floor in my shed. Although my charging location is relatively safe, I always monitor my batteries during the charging process.
We have all been in that situation before, leaving your batteries to charge unattended. Thinking that ‘they will be alright’. Whilst this is true most of the time, it only takes one unlucky occasion for your drone battery safety to turn on its head. For this reason, I recommend always monitoring your batteries and keeping them in close proximity to yourself. This is the most essential of all drone battery safety precautions as a quick response time to a failing LiPo can be the difference between losing a single battery pack or your entire house. If you notice a charging LiPo puffing, smoking or catching fire, you should attempt to unplug the charger from its power source if it is safe to do so.
Following on from battery monitoring, having a method of extinguishing a battery fire is a wise idea. I recommend purchasing a fire extinguisher and storing it near your LiPo charging setup (but not too close as you want to be able to access it if a LiPo catches on fire). A LiPo battery is classed as a type B liquid fire due to the internal gel/liquid electrolyte solution. Hence, to extinguish a type B fire, an ABC/ABE type dry chemical fire extinguisher should be used. Other methods to extinguish a LiPo fire include the use of carbon dioxide (CO2), a foam extinguisher, or sodium bicarbonate. Pictured below is the ABE dry chemical fire extinguisher used at my local drone club.
LiPo Charging Bags
To minimise the potential damage from a LiPo fire, charging bags are a cheap and effective solution. Charging bags do not easily burn because they are made from a flame-resistant material. I always recommend storing LiPo batteries in charging bags regardless of whether the packs are being stored, charged or transported. Charging bags are also an essential when traveling on aeroplanes with LiPo batteries. In the situation that a LiPo fire does occur, the charging bag should contain the fire however it will still vent dangerous battery gasses which you should not inhale. The video below by Buddy RC demonstrates the effectiveness of a LiPo bag.
LiPo charging safes are even more effective then LiPo bags at containing a battery fire. Although charging safes are more expensive then charging bags, I would say that their increase in drone battery safety validates the price. Ideally, you should use a LiPo safe for charging and home storage coupled with a LiPo bag for battery transportation when going flying. My personal favourite charging safe is the Batt-Safe which can hold quite a few batteries and incorporates venting holes into the design. Venting holes are important as an airtight safe could burst open from the pressure of the LiPo battery gasses released during a battery failure. The video below from Michael Niggel demonstrates the effectiveness of a LiPo safe.
Homemade Charging Safe
If you would like to make your own charging safe, I recommend using a powder coated steel toolbox. Wallmart has quite a wide variety of toolboxes in various sizes. The powder coating acts as a layer of insulation between the batteries and the toolbox. After purchasing the box, all that is left to do is to drill a small hole and install a rubber grommet so that charging cables can be fed into the box. Commercially available charging safes are generally safer than homemade safes however any drone battery safety is better than no drone battery safety.
One of the best preventative drone battery safety measures is to purchase high quality chargers. High quality electronics will fail less often then cheaper products and quite often have better failsafe mechanisms in place to prevent catastrophic failure. ISDT is my personal favourite brand of chargers however anything sold by GetFPV should be a high-quality product.
Monitoring Battery Condition
There are several methods of determining the condition of a battery. By simply flying with a LiPo, an advanced pilot will be able to roughly determine the condition. After a flight, you can also use a charger or battery checker to observe how closely matched each cell’s voltage is. If there is a 0.1 volt or greater cell voltage difference, the battery may be nearing the end of its life. My favourite method is to use the battery internal resistance checker on my ISDT charger (pictured below). A good quality battery will have an internal resistance lower than 10 milliohms per cell. Once the internal resistance exceeds 20 milliohms, I will usually retire the battery from racing. To learn more about battery condition and LiPo care, you can read Josh’s article here.
To properly dispose of a LiPo, the safest option is to first discharge the pack using a battery charger and then to connect the power leads to a 12V incandescent light bulb for several hours. This will ensure that the LiPo is fully discharged to 0V. As entertaining as the fireball looks, it is not wise to dispose of a LiPo by puncturing or damaging it. Once the LiPo has been discharged completely, it is ideal to cover over the battery terminals and take the pack to your nearest battery recycling facility in order to reduce the overall environmental impact.
I hope this article has been useful in educating you about drone battery safety. If you take the correct drone battery safety precautions, LiPo battery charging and storage can be completed safely and effectively with minimal risk. Click here to learn more about LiPo batteries.