FPV Battery Safety
Written by Kevin Bowery
We all have heard the saying “safety first,” but when it comes to FPV battery safety it is difficult to be too safe. Broadly speaking, the batteries FPV pilots use are made up of individual cells containing a positive and a negative electrode, a thin membrane between electrodes, and an electrolyte. When the battery is charged the positive electrode gains ions and when discharged it loses the ions to the negative electrode. The electrolyte helps facilitate ion transfer, and the membrane prevents the electrodes from touching. If you think back to chemistry class, you may recall that lithium is a very reactive element. This makes it super effective at storing energy for rapid discharge, but what happens if the electrodes touch? Fire. Lots of fire! What’s worse than fire? A SELF-SUSTAINING FIRE.
The warning signs
Fortunately practicing good FPV battery safety can prevent your quads (and even your house) from becoming extra crispy. Even in the best conditions, there is a chance of spontaneous thermal reconfiguration. The good news is that batteries give some warning signs including:
Swelling of one or more cells
Physical damage to the cells
One or more cells reporting substantially higher or lower voltages than other cells when connected to a battery monitor
Extreme heat after landing
Liquid appearing on the battery after flight
A sweet smell (like candy)
If you notice only one of these signs, proceed with caution. Let the battery sit aside where it cannot easily start a fire. If more than one of these signs are present, quickly get that battery away from anything important!
Crashes have Consequences!
Many of these indicators show up after crashing. Those photos are from a practice session where my friend Dylan hit a pipe at full throttle. The cells punctured on impact and immediately started burning. The fire was so hot his props melted! Also pictured is battery of mine that over discharged when I was flying. Notice how the cells are so puffy that they have split the heat shrink apart.
FPV battery safety in flight can be increased by taking steps to protect the cells. Some people cut up an inner tube and stuff the battery in the soft rubber sleeve. The only problem is that you cannot see some of the other physical indicators. You can wrap the battery in a couple extra layers of clear heat shrink. Alternatively, you can 3D print a protective case that covers the exposed sides of a battery. Search on thingiverse for a “LiPo protector” and you will find something that fits your needs.
FPV Battery Safety at Home
The first thing you should do is purchase a container for your batteries. In my experience I have found soft LiPo bags and 50 caliber ammo cans to be the most effective storage vessels. NEITHER WILL FULLY CONTAIN A FIRE. They just give you extra time to recognize and react to a problem. This can be as simple as grabbing the handle and throwing the whole case to a less flammable location. Take for instance: One day at work I was charging a large 6S battery that had been over discharged. The charger indicated there was a cell falling wildly out of balance. I slammed the lid of the ammo can down and ran out of the building with an ABC fire extinguisher. The image below is the remains of the battery, ammo can, and the board the ammo can was placed on. The fire extinguisher did nothing to put out the LiPo but managed the secondary fire caused by the heat from the ammo can.
After this incident, my boss wanted to see what would have happened if we had not acted in time to get the battery outside. We took another large LiPo outside to the loading dock and punctured it. If those pictures have not convinced you to buy a proper container, this video I recorded shows the same battery without any protective containment: https://www.youtube.com/watch?v=owrLRRH7KlI
Safe Charging Guidelines
Keep the batteries safely charged and stored. These are the standard recommendations pilots adhere to:
Do not leave batteries unattended when charging or storing. If something were to happen, you should be there to try and mitigate damage.
Do not leave the batteries charged above 3.80V per cell. Battery cells can stay at this voltage almost indefinitely and not lose substantial performance over time.
Do not charge at the rate of more than 1C. Calculate this by taking the milliamp hours (mAh) and dividing by 1000. For example, a 1300mAh 6s LiPo should be charged at a maximum of 1.3A
Do not charge batteries above 4.20V per cell, any higher can cause spontaneous combustion.
Keep the batteries in the case you purchased when you are not using them.
Keep the storage container(s) in a cool, dry space. It is not sensible to leave them in a hot car, or in the summer sun.
Final thoughts to cultivate FPV battery safety
Even if you follow these recommendations, you still may come across a dangerous battery. The tempting thing may be to puncture the cells with a sharp object, or bend the damaged cells back into shape. This is risky since both options may cause a fire. You could just fly the battery until the quad falls out of the sky, but that can damage your gear.
The safest way to dispose of a bad battery is to get a large plastic container, create a saltwater solution, and head outside. Gently place the battery in the solution. It will start bubbling and will stop once the battery is completely dead. Just leave the container outside overnight and then throw the dead battery in the trash or bring it to a battery recycling location. You can find one by googling “LiPo Battery Disposal Near Me”. FPV battery safety is not the most enjoyable part of the hobby but investing a little bit of effort and following the guidelines, you significantly mitigate the risk of an accident so you can fight against gravity without wings! (That’s the MultiGP slogan by the way!)
