The inevitable question for RC hobbyists is how to get rid of old or damaged lipo (Lithium polymer battery). There are tons of Youtube videos showing how dangerous lipo batteries can be if not handled correctly, causing explosions and fire flames. So how do we dispose damaged or old lipo batteries safely?
Created in Oct 2014, updated Jul 2016.
First, discharge them completely down to 0 volt, then cut the discharge lead and twist voltage and ground wires together to ensure there is no charge left in the pack. Finally wrap them with paper and put in the dustbin, or better, bring them to recycle centres. You might have a different way, please let me know in the comment.
There are many ways to discharge the battery before disposing them, I will introduce you a few easy and common ways here. If your battery is damaged, it’s the safest to use the “Salt Water” method.
# Discharger Method
If your lipo charger has a discharge function, you can use it to discharge your battery. But some dischargers has a minimum voltage limit, e.g 3V. That means it might not discharge your battery completely. But this seems to be a fast way of discharging your battery. Remember always discharge it at small current just to be safer, e.g. 1/10 C, for a 2000mAh 50C, discharge at 2A/10 = 0.2A.
Note that do not discharge the battery with your charger if it’s damaged.
# Light Bulb Method
Light bulb is a very popular tool for discharging lipo battery, because it’s relatively quick, cheap and effective. For example for a 3S Lipo, you can use a 12V light bulb, and just leave it somewhere fire proof.
Here I built a Halogen Bulb Discharger.
Try to avoid LED type of light bulb, they have “forward voltage” which means when voltage drops below a certain level, it will simply stop discharging, and you will still have a small amount of charge remains. Also LED are relatively energy efficient which means it will take longer to discharge. It’s best to use Halogen bulbs.
You can also use some kind of resistive load instead of light bulb, for example a motor. For 2S or 3S Lipo, you can also use 150omh 2W resistors.
# Salt Water Method
This could be the slowest method if your battery wasn’t discharged previously by the above methods. Some discourage from using salty water because it’s time consuming, but I personally think it’s a relatively easy and safe solution. No matter what, I always go through this step before dumping my lipo.
The theory behind this is 1 – salty water is electricity conductive and it discharges the battery slowly and completely; 2 – salt causes chemistry reaction with the substances in the lipo battery, and neutralizes the Lithium. I am not a chemist, so I hope someone can verify this theory.
- Get a plastic container which you can afford to throw away, and fill it with cold water.
- Mix it with salt and make sure it’s dissolved completely. I always use about 30g of salt per litre of water and that has been giving me good result.
- Put the battery in the salty water, and leave it somewhere fire proof for two weeks. Depending how much charge it had originally, you might want to leave it longer.
- Finally, wrap the battery with paper and it’s ready to be thrown away.
Also note that salt water might not completely discharge your lipo, as corrosion can happen and reduce/stop electrical conductivity (the exposed metal on the leads will have a layer of insulator building up in salt water). Eventually it would slow down, or even stop the discharging completely.
# Physical Destroy Method
This is the least recommended method because it’s dangerous. Actually, I don’t recommend it at all. I have read some people use guns to shoot through the battery, use nail to puncture them, or use hammer or brick to break it and let it ‘explode’. This is probably the quickest method, but fire hazardous and the smoke is not good to breath in.
How do I do it?
Personally, I prefer to use a halogen light bulbs discharger to completely discharge the pack first, then I cut the connectors and twist the discharge leads together to ensure there is no energy left in the pack (+ and -). This way it normally only take less than an hour which is far more efficient than dipping the battery in salt water for weeks.
It’s useful to save the connectors especially the balance lead, if you have one damaged on a good pack you can use it for replacement.
A few tips on using Lipo
- Always charge Lipo battery supervised
- Always use the balance charging (balance plug)
- Always use a lipo-safe bag if you have one
- Always dispose lipo batteries properly.
- NEVER short a lipo battery.
- NEVER try to use damaged or puffed up lipo batteries.
- NEVER over-discharge a lipo, it will reduce the life span, and might cause safety issue.
Follow these methods at your own risk, and do everything necessary to prevent fire. Consult a professional if you are in doubt. Keep away from human and animal when you are doing any of the above.