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May 24, 2021, 10:07 AM
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Are Your Lipos Safe? Tips From Team Hobbyking


From HobbyKing...

The most common questions we get regarding LiPo batteries are: “Is my LiPo battery safe to use?”, “How do I know if my LiPos are damaged beyond repair?”, and “How long will my LiPo batteries last?”

What Causes Puffing Or Swelling In LiPos

You may have heard people tell you to chuck your LiPo in the bin if it starts to puff up. While only partially correct, all LiPos will inevitably show some degree of swelling. So, the real question here is: why do LiPos puff up?

A LiPo battery is made of three main components: the positive electrode (cathode), the negative electrode (anode), and the liquid electrolyte. Electrolyte is a chemical inside your LiPo that enables the flow of ions from the negative end to the positive end during discharge, and vice versa when charging.

Your LiPos puff up due to a naturally occurring phenomenon known as electrolyte decomposition. When electrolyte decomposes, hydrogen, carbon dioxide, and carbon monoxide are formed as by-products. These gases are not only responsible for the physical swelling of your LiPos, but two of the three are also highly flammable.

Electrolyte decomposition will occur regardless of how you handle your LiPos. So, going back to our first question, should you dispose of your LiPos if they start to swell up? The correct answer is - it depends. When properly cared for and used responsibly, electrolyte decomposition will still take place, however, at a much slower rate. If you only had your LiPo for a brief period and it swells up exponentially, then you are either doing something wrong, or the LiPo could be faulty - under this scenario, we will recommend you to safely dispose of it.

On the other hand, if your LiPo has gone through 50+ cycles and starts to show some swelling, we would consider this to be perfectly normal and would not recommend you retire it just yet. In theory, a swollen LiPo can still be fairly safe to use if everything else is intact and working properly. As noted, two of the three gases – hydrogen and carbon monoxide – are highly flammable and can become dangerous if there is a heat spike, or if exposed to air; both can be attributed to external factors which will be discussed below.

Physical Signs Of Damage

One of the first and most obvious ways to determine if your LiPos are safe to use is to physically examine them. A physically damaged LiPo, combined with swelling is really just a ticking time bomb. Most, if not all LiPo accidents happen for one reason: a punctured inner foil. When punctured and exposed to air, the mixture of gases and lithium ions will ignite and even explode.

After every use, check your LiPos for any glaring impairments. If you just came out from a hard landing with your RC aircraft or completed a bumpy ride on your basher, pay extra attention to surface dents, deformities, cracked wraps, wrinkled cells, and any damages to the battery connectors.

Internal Resistance

One of the best and more accurate ways to determine if your LiPo is functioning properly or not is to check the internal resistance (IR). IR ultimately dictates how efficient your battery is. A low IR implies greater efficiency while a high IR means the opposite. Just like electrolyte decomposition, IR will gradually increase over time, however, proper usage can significantly prolong the process.

A high IR will cause your LiPos to heat up very quickly while delivering a lower voltage; in layman’s terms, it would mean that your LiPo is working two times harder while only delivering half of the results. Continued usage of a LiPo with a high IR will ultimately cause it to heat up and expand to a certain point where one of the inner cells may rupture causing it to explode.

When you first purchase your LiPo measure its IR. Generally, an increase of around 80-90% would indicate that your LiPo is nearing its end and you should probably dispose of it. So, for example, if you had an initial IR of 10 mΩ and after 150+ cycles the IR reads at 18 mΩ, this would suggest that your LiPo should be retired sooner rather than later. In Conclusion... As with most things, nothing is ever 100%. However, next time you reach the crossroad of deciding whether your LiPo is near its end or not, you could use these simple steps:

1. When you first purchase your LiPo, label it with the date of its first use. Using this date, you can gauge if the swelling is proportionate to its usage. Generally, HobbyKing’s LiPo batteries can last 2-3 years on average.

2. Check for any obvious damages that may be detrimental to the inner wrapping of the cells. This may include, but not limited to the following: surface dents, deformities, cracked wrapping, wrinkled cells, and damaged battery connectors.

3. Using a smart charger or battery meter, check that the IR is not overly high. Even if only one of your three cells has an off rating, discontinue using it as any rupture to any of the cells can lead to a major disaster.

HobbyKing's Tips Bench Tuesday - How To Determine if Your LiPo Batteries are Safe (7 min 25 sec)

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Last edited by Jim T.; May 24, 2021 at 10:15 AM.
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May 24, 2021, 05:01 PM
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Miami Mike's Avatar
Great info!

What do I need to measure internal resistance if my charger doesn't have that function?

What are some typical values to expect?
May 25, 2021, 12:19 AM
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rampman's Avatar
Originally Posted by Miami Mike
Great info!

What do I need to measure internal resistance if my charger doesn't have that function?

What are some typical values to expect?
This is considered the golden standard of an internal resistance meter.

There is no single number because the internal resistance varies depending on the size of the battery [mAh] and temperature.
Wayne Giles and a few other experts in lipo IR suggest 72F if possible.
If not you need to be consistent in your testing temperature.

May 25, 2021, 08:16 AM
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Miami Mike's Avatar
Okay, thanks! Before I clicked your link I shortened it to this by removing everything beyond the "html". That's all that's really needed, the extra 192 characters are just tracking data.

I can buy quite a few new LiPo batteries for $149.00, so I think I'll pass of that meter. But if there's a cheaper way to measure internal resistance, such as a home-made setup, then I'd be interested in that.

And I'm sure there's a formula to determine what internal resistance to expect based upon the other known or claimed data about a LiPo pack. I realize that if you measure packs when they're new you'll have a reference for later, but I don't have that and I want to evaluate packs that I've owned for a few years.
May 25, 2021, 06:45 PM
Space Coast USA
hoppy's Avatar
Search youtube, many methods using simple meters. Not the most accurate but probably good enough for tracking the decline of your packs over time or separating good packs from bad packs.
LiPo INTERNAL RESISTANCE (13 min 30 sec)

LiPo INTERNAL RESISTANCE TESTING - a simple 12v load tester (17 min 37 sec)
May 26, 2021, 05:35 PM
I like twins!
kajukenbo's Avatar
Gosh, isn't the magnitude of the resistance important, and not just the % change? A 2-4 mΩ change is 100%, but much different than a 10 mΩ to 20 mΩ Am I mistaken?

What does "overly high" mean?
Last edited by kajukenbo; May 26, 2021 at 05:41 PM.
May 26, 2021, 07:06 PM
Registered User
Very good information BUUTT

I do not need to check or worry about any of the bad indications of a LIPO in trouble. Ever

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