HobbyKing Tips - 3 STEPS TO DETERMINE IF YOUR LIPOS ARE SAFE

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?”

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Are Your Lipos Safe?

All these questions have the same underlying theme: safety. Today, we will take a deep dive into the chemical properties of LiPos and learn how to spot a perfectly functioning LiPo, from a faulty one.

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

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.

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Sep 13, 2021, 04:26 PM
Tommy Toy the Crazy Boy
I measure the IR of every cell of every battery about every six months.

What should a normal IR be on a brand new battery?

At what IR should I think about replacing the battery?

Thanks,
Tom
Sep 13, 2021, 09:05 PM
Recreational Model Plane Pilot
Rhea's Avatar
I just record the IR of new batteries and monitor them periodically to see if it is changing.

My unscientific observations are that it doesn't change much over time but it might be because I don't abuse them so they will last a long time.
Sep 13, 2021, 10:32 PM
Tommy Toy the Crazy Boy
Thank you.
Sep 15, 2021, 01:55 AM
Registered User
scott page's Avatar
Quote:
Originally Posted by tmulligan
I measure the IR of every cell of every battery about every six months.

What should a normal IR be on a brand new battery?

At what IR should I think about replacing the battery?

Thanks,
Tom
The acceptable IR is different depending on the size of the battery. Smaller capacity batteries will have a higher IR -- so obviously -- larger capacity batteries have lower IR. For NEW batteries -- I'd like an IR of near 1.0 mΩ for larger batteries near 5000mah and about 2.2mΩ for 2200mah.

There is a fantastic online tool where you can plug in the IR and size of the battery and it will tell you how many amps that battery should be good for.

http://jj604.com/LiPoTool/
Last edited by scott page; Sep 15, 2021 at 02:00 AM.
Sep 15, 2021, 05:00 PM
Tommy Toy the Crazy Boy
Thank you. The specifics are what I needed to know.

Tom
Sep 16, 2021, 11:41 AM
Registered User
E-Challenged's Avatar
Is there a way to check IR per cell using a simple multimeter? Most chargers do not have IR checking feature.

Never mind, just read posts about new version of IR meter below and have headache. I have an old Cellpro 10S charger that gave cell IR readings but doubt whether it and FMS software still works.
Last edited by E-Challenged; Sep 16, 2021 at 12:26 PM.
Sep 16, 2021, 04:46 PM
Registered User

Long ago. A123 Gave the IR or their cells.


I never had or measured the I R. I knew how many minutes of recharge it took at the 4 ampere rate. Those ancient cells are taking 20 % longer to recharge & balance. Good enough for my purposes.
Sep 23, 2021, 10:03 PM
Lurking......
LTR91's Avatar
Hot tip- do a sniff check: the electrolyte has a distinctive sweet odor. If you smell this your battery is defiantly bad. Even if the voltage looks good, within a day or two the cell will go flat.

I've had a few packs on my drone that received minor nicks to the side of the pack, which looked fine. The only way I knew something was up aside from the cut in the plastic was that sweet smell.
Sep 24, 2021, 12:09 AM
Registered User
scott page's Avatar
Quote:
Originally Posted by LTR91
Hot tip- do a sniff check: the electrolyte has a distinctive sweet odor. If you smell this your battery is defiantly bad. Even if the voltage looks good, within a day or two the cell will go flat.

I've had a few packs on my drone that received minor nicks to the side of the pack, which looked fine. The only way I knew something was up aside from the cut in the plastic was that sweet smell.
I throw them in a zip lock bag overnight and then open the bag -- the smell is unmistakable.
Oct 26, 2021, 09:29 PM
Registered User

Mr.


I was given a older airplane that had Lipo 1800 30c 11.1v 20Wh. I have been trying to locate such battery or a equivalent to it. I would appreciate any help with this matter. Thank you in advance
Oct 26, 2021, 09:32 PM
Registered User
scott page's Avatar
Quote:
Originally Posted by Hank53
I was given a older airplane that had Lipo 1800 30c 11.1v 20Wh. I have been trying to locate such battery or a equivalent to it. I would appreciate any help with this matter. Thank you in advance
Here you go. Two options -- one with XT60 connector, and one with EC3 from a very good brand with excellent prices. By the way -- this is a 25C battery - however today's 25C from this company actually has much less resistance than "30C" batteries from the past, or from most other manufacturers.
https://rcbattery.com/batteries/plan...city=1655-2181


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