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How To Tell If An RC Battery Is Bad?

If you have had an RC car, plane, or drone for very long you have probably wondered at some point how you can tell if the battery is starting to go bad. After all you’ve probably seen the horror stories online about batteries exploding and of course you want to prevent that from happening to you and your battery but how do you know if your battery has gone bad? When is it time to replace it? 

There are three main things that you can look for to determine if the battery is dead. Those are 

  1. If the battery is swollen 
  2. If the battery capacity is less than 80% of new
  3. If any cell in the battery is below 3v (LiPo batteries)

The most likely and noticeable sign that your RC LiPo battery is bad or going bad is that it begins to get puffy. Once a battery starts to puff it it should not be used again and should be properly disposed of immediately. 

Some people say that letting the battery cool before use will allow you to continue using it and while that might be true in some circumstances you are also opening yourself up to a possibility of a battery fire and destroying your RC vehicle entirely. 

With NiMH batteries, the easiest way to know if your RC battery is bad is by checking if the voltage is the right amount after a full charge. This could also apply to LiPo batteries. If it’s not as it should be, then there’s likely a problem with one of the cells going bad which in turn means your battery pack is going bad to. 

Another thing to look out for is the way the battery runs. If it runs slow for an extended period of time, then there’s a high likelihood that it’s bad. Try charging it slowly a few times to check the conditions of the pack.

If you would prefer to watch a video on this subject instead you can do so below. To see the best RC batteries on the market just click here.

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So, what can you do to fix a bad RC battery? 

Unfortunately there’s really nothing you can do to fix a bad RC battery. If an RC battery is bad, especially a LiPo, the safest thing to do is discharge it and dispose of it properly. Many hobby shops will accept bad batteries but you can also soak the battery in salt water and then throw it away yourself as well. 

Seeing as LiPo batteries mostly swell up as a sign of damage, trying to fix anything could put you at such an incredibly high risk that it’s definitely not worth it. There’s no point burning down your house or getting yourself injured just because you were trying to save some money. 

The ideal thing to do with a swollen LiPo battery pack is to first discharge the battery and then go on to dispose of it.

Disposing of Your Lipo Batteries

Disposing of your LiPo batteries requires you to do a lot more than just throw the batteries away. Merely throwing the batteries away may even be fatal! There are two major methods you can use to discharge an RC battery, hooking it up to a light bulb, and putting it in a bucket of saltwater.

If you are using the light bulb, it is best to use the 12 V, 20 Watt halogen bulbs. These bulbs are easy to solder to so it is much simpler to attach lead wires and connectors. This, in turn, makes it a simple thing to just plug in your battery and let it discharge. You can hook multiple in parallel to allow you to get your preferred discharge rate.

As soon as you have completely discharged your battery, go to the battery recycling drop-off point nearest to you and drop it there. Make sure that you call ahead to find out if they accept damaged batteries. Also, visiting your local hobby shop will certainly make the entire process of discharging and disposing of a lot easier and more straightforward.

The salt water bath is the preferred option for many people since it’s much easier than hooking the battery up to a light however many people have reported that it doesn’t work well to actually discharge the battery and other people have even reported that the battery still ended up on fire inside the salt water bath! 

If you have the capability to drain the battery via the light bulb method then you will certainly want to go that route as it is considerably safer in most cases. 

How to Prevent Your RC Batteries from going bad? 

Seeing as having a damaged battery pack will require you to dispose of your batteries, you might want to put some more effort into making sure that the batteries do not get swollen or damaged in the first place. So, here are some things that you can do:

Charge the batteries properly

Make sure that you use a quality charger and properly charge your batteries. Having your battery in a LiPo bag when you’re charging provides a lot more safety, so consider getting one as soon as possible. Using a LiPo bag minimizes the chances of any hazards, and in the event that anything goes wrong, it is, at least, contained.

Don’t over-discharge

 Be sure to stop discharging your battery before the voltage gets to the minimum cut-off voltage. Most RC cars have a system in place to prevent over discharging. They are typically called low voltage detection or something similar. 

Be cautious of heat

Do not use or charge your batteries when they are hot. When you have finished using them, give the batteries some amount of time to cool off before you charge them. When you have finished charging the batteries, give them some time to rest before you start using them again as well.

Store properly

Storing your batteries in a hot place is a complete no-no. During the summer, for example, do not keep those batteries in the trunk of your car and also make sure that your LiPo batteries are stored at the proper storage voltage. Storing your LiPo battery in the wrong place greatly increases the risk of swelling, so you should be careful about where you store the batteries.

When it comes to LiPo batteries, always remember that if they are used wrongly, especially as they get older, gases will start forming in the batteries, and swelling is the end product of this. Once you see that your LiPo battery is puffed up or swollen, the very first thing to do is completely discharge it and then properly dispose of it. Resist the urge to fix a swollen LiPo battery because you’re just going to be setting yourself up for an injury. 

Never forget, also, that your local hobby store is a trustworthy place to discharge and dispose of bad RC batteries, so you might want to choose that for safety purposes.

What about NiMH batteries? 

Speaking of NiMH batteries, when they die, apart from just disposing of them, you may also choose to revive them and let your batteries have a longer time with you. So, here are 2 simple steps to reviving your NiMH batteries;  

First step: Checking the battery

The first thing to do is check if the battery still has any juice left in it after you have charged it for some time. This is to help confirm whether or not the battery is dead.

Second step: Reviving the battery

This step requires you to take a fully-charged similar battery of the same mAh. Next, connect the positive terminal of the fully charged battery to the positive terminal of the dead battery and connect the negative terminals in the same way.

Allow the batteries to stay connected for a few seconds (about 20-30). Check the voltage of the dead battery right after, and if you see a reading higher than the 0 value, the battery has been revived.

If the battery is not revived after this, repeat the process a few more times, and it will likely work. If you still face any issues, check to make sure that the battery you’re using to revive the dead one is actually fully charged. When the battery has been revived, charge it till it gets full.

This will only work on some NiMH batteries but typically this type of battery lasts far longer than LiPos although they offer much less power than LiPos do. 


If your RC battery is swollen or has less than 80% capacity then it is considered to have gone bad. You can still use a NiMH battery that is below 80% without any issues besides shorter run time but once a battery has started to swell up it should not be used ever again. 

A swollen battery is a danger to your RC car and your safety so if you notice your battery starting to feel a little “puffy” the next time you charge it then it’s time to dispose of it properly and replace it.