Inevitably, one of your LiPo batteries is going to fail. Whether it gets cycled one too many times or puffs up from a particularly bad crash, eventually you will be left with a battery that is no longer safe to use. Even with proper care in charging, most LiPo batteries won’t last longer than a year or two if you fly consistently a few times a week.
When you determine a battery is no longer flyable, it’s time to discharge the battery and safely dispose of it. This article will cover multiple methods for safely discharging a LiPo battery, as well as options for disposal. We highly recommend checking local laws and regulations where you live before undergoing any of the processes described below.
Discharging a LiPo battery safely
Safety is key here. In many cases, you will be working with an unstable LiPo, and need to be very careful. We recommend reviewing our “How LiPo batteries explode article” before discharging your first LiPo.
No matter what methodology you use, always discharge your battery in a safe location. If possible, we recommend completing this process outside using a battery bunker. If you are discharging damaged batteries, please take extreme caution to protect yourself and property before following any of the steps below.
Using your battery charger as a discharger
Most battery chargers on the market have a discharge function that you can use to safely discharge a LiPo battery. Switch your charger’s setting from “Charge” or “Balance Charge” to “Discharge”, set a low current of .5A-1A, and go! This is a fast way to safely discharge LiPo batteries that are at the end of their lifespan.
There are a few things to keep in mind though. Most battery chargers will not completely discharge the battery, as usually the discharge cycle will discharge the battery to a minimum voltage. The reason is that these features are generally intended to take the battery to the minimum safe voltage before damage occurs, not to totally disable the battery. When disposing batteries, you want to do the latter.
For this reason, we recommend using one of the alternative methods discussed below to discharge your “dead” batteries. If you do decide to use your charger to discharge a damaged LiPo, do it outside and away from flammable materials or use a battery bunker of concrete cinderblocks or a vented ammo box.
Using a halogen lightbulb as a LiPo discharger
A light bulb discharger is a great tool to add to your work bench. These can be built very cheaply and allow you to discharge a LiPo battery nearly anywhere. The theory is simple: a lightbulb will slowly drain your battery down to a safe voltage. If the battery is drained so much that it can’t power a lightbulb, it’s going to be safe to discard.
Building one is simple. All you need is an XT60 male connector, two wires (we used the same gauge as our batteries: 14AWG), a halogen lightbulb (we like 12V, 20W bulbs for landscaping or car taillights), and some heat shrink and solder.
Why a halogen lightbulb? LED bulbs are too efficient, and will take longer to complete the process. You can pick up halogen bulbs off Amazon or nearly any hardware store very cheaply. The downside is these batteries will get very hot while undergoing the discharging process.
- XT60 connectors (Amazon)
- 14 AWG wire: red and black (Amazon)
- Heat shrink (Amazon)
- Halogen lightbulb (Amazon)
Rough build price
|Part||Price per pack||Price for discharger|
|XT60 connector (male)||10 pairs [10f/10m]/ $6.99||$0.35 (1 connector used)|
|14 AWG wire||10ft [5r/5b] / $8.48||$0.85 (1ft wire used)|
|Heat shrink||48pc set / $5.99||$0.25 (2 pieces used)|
|Halogen lightbulb||10 bulbs / $6.39||$0.64 (1 light used)|
|Total:||$29.85 shipped Prime||$2.09|
Prices may change due to Amazon listings, but these are the prices at the time of writing.
All of the above options are Amazon Prime applicable, so shipping would be included. Other than the lightbulbs, all these items are very useful for quadcopter repairs and will last you across multiple builds. In fact, you may have most of these components already if you have been in the hobby for a bit!
The other neat thing about building a LiPo discharger is that you can use a spare bulb to also build yourself a crude smoke-stopper. Two-for-one!
- Fill male XT60 connector cups with solder. Cut, strip, and tin wire.
- We like using 3 to 6 inches (7.6 to 15.2cm) length of wire for this depending on your setup.
- Solder wires to XT60 connector: red to positive cup, black to negative cup.
- Fit heatshrink over other end of wires and shrink in place over soldered points at the XT60 connector.
- Solder lightbulb to wires by inserting the prongs into the wire strands and adding solder. Wire ordering doesn’t matter here, just make sure the positive and negative wires aren’t touching. Do not use heat shrink – it will burn as the light can get extremely hot.
We recommend using at least 3 inches or 6cm of wire. If the light burns out, simply snip the wires back a bit to release the lightbulb and solder on a new lightbulb.
You can get more advanced with your lightbulb build if you want. You could use a breadboard to make the lights hot swappable, or even solder together a few lights to increase the draw for larger batteries. However, the above build process will work for nearly all 3S and 4S batteries, will take you only a few minutes to complete, and is the cheapest setup to make.
Using the lightbulb discharger
Now that you have your completed discharger, how do you use it? Plug the battery you want to discharge into the discharger, and the lightbulb should glow. Simply wait for the lightbulb to go out, and the battery is discharged! It’s that easy!
Now, just like using your charger, there are a few caveats. First, the lightbulb will get VERY hot. We measured 350C with our infrared gun! This is easily hot enough to burn you instantly and maybe hot enough to cause spontaneous combustion should you place it on some paper or something. Make sure you choose a location for discharging that is heat resistant (again, we recommend a cinderblock bunker or ammo box).
If the heat is a concern, it’s safe to operate the light inside of a jar of water to burn off the heat. The problem with this is that the wires on the bulb will galvanically corode over time and you will have to replace the bulb every 5-10 batteries. While not our recommended method, this could work in a pinch if you are at the field and don’t want to transport a damaged battery home and is pretty neat to boot.
Discharging with a salt water bath
A final method of discharging your battery is to submerge it in a salt water bath for a long period of time. By doing this, the battery will slowly discharge to a completely dead state. The process is simple. Grab a plastic bucket, fill with a mixture of water and salt (at most 10:1), fully submerge the battery in your salt mixture, and place the bucket someplace fireproof. Salt water is conductive, and should slowly discharge the remainder of the battery. After a day or two, the battery should be fully discharged.
This method can also be used if you absolutely want to remove all the excess voltage from a battery and get as close as possible to that 0.0V number. However, it should not be used for batteries that have physical cell damage like punctures.
You may be thinking, “why would I take the time to make a light bulb discharger or risk connecting an unsafe battery to my charger if I can just toss the battery in a salt bath and walk away?” It really has to do with patience. You’ll need to let your batteries soak for a long time to fully discharge them, while the light bulb method can get them to a near-dead state in a matter of minutes. Furthermore, larger capacity batteries can galvanically destroy the open connectors / wires before completely discharging the battery, leaving it still charged and unsafe.
What to do if you need to discharge a battery with a broken XT60 connector?
Discharging via a charger or lightbulb will be somewhat difficult if you shattered your XT60 connector on a bad crash. What should you do in this case?
You have a few options. Arguably the easiest option would be to take a spare female XT60 connector and reattach the battery wires. After salvaging a few batteries, you should have plenty of these connectors lying around. Similarly, you could just solder the light directly to the battery.
Either way, be sure to take precautions so that the positive and negative wires of the battery do not touch. We like wrapping one wire in electrical tape or heat shrink while working on the other. This should prevent crossing the wires.
Before tossing your battery into the trash can or salt bath, you may want to salvage the remaining unbroken connectors. Having a spare bank of XT60 and balance connectors can come in handy for repairing batteries in the future.
To do so, carefully use wire cutters to cut the connectors away. We like cutting each wire at an angle one at a time to prevent the wires from touching.
We recommend discharging the battery first, then removing any connectors before putting your battery in a salt bath. Similarly, you can cut these angles close to the battery to salvage the wires! The LiPo discharger I built for this articles used salvaged battery wires. If you have a bunch of spare parts around and can salvage some wire, you can make a discharger extremely cheaply!
If your balance leads are undamaged, you can salvage those as well. Don’t bother if they are cracked or split in any way.
Salvaging working cells
This is a question that comes up on a lot of forums and battery discharge videos. Let’s say that you test your battery and maybe only one cell is broken. Theoretically, you could remove the other cells and make a new battery for a smaller quad, goggles, etc.
Do we recommend this?
No. For most pilots, we do not recommend trying to salvage working cells. I am sure there are a few people that will balk at wasting what could be perfectly good cells, but for most hobbyists we do not think the value outweighs the risks.
There are plenty of other resources around the web for recovering cells from broken batteries, and you are absolutely welcome to Google around and check them out if you are interested.
Discarding the battery
Alright, so your battery has been safely discharged and you are ready to get rid of it. How should you do so?
Take to a local hobby shop or electronics store
Our personal favorite way of discarding batteries. Many hobby shops and electronics stores offer battery recycling boxes that you can use to safely discard your battery. Drop your discharged battery in the box, and you are done.
Take to a disposal center
Lastly, you can take the battery to a local electronics disposal center. Depending on your city, these may revolve to different locations, or are contracted out to a specific store or junkyard. Check your city’s website for more details. Unlike the other options, we have found that some disposal centers may carry a charge for destroying the battery, so if you can, we recommend calling ahead to ask if that’s the case.
Throw it in the trash can… maybe
Depending on your locale, you may be able to throw a fully discharged battery right in your home trash can. However, this varies greatly from country to country, state to state, and even city to city. Check your local laws before throwing any batteries in your home trash. If your local laws aren’t specific on LiPos, you can always call your garbage service for more information and recommendations.
A final word: don’t nail puncture a battery
An old style of neutralizing a battery was driving a nail through all the cells.
Don’t do this at home, kids. This is a very unpredictable method, and can result in lighting your battery on fire, or worse, an explosion.