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Lithium Polymer Etiquette: A Comprehensive Guide to Working with LiPo

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Picture of Lithium Polymer Etiquette: A Comprehensive Guide to Working with LiPo
In this Instructable I will be going over the basics of proper charging, discharging, handling, usage, storage, and care of lithium polymer batteries so you can use them safely and effectively in your future projects.  Now, this is by no means the be-all and end-all of information, and it's always important to consult the instructions for your specific equipment, but I think this Instructable will provide a good basis of knowledge on the subject of these awesome batteries.
 
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Step 1: Terminology

Picture of Terminology
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If you're new to lithium polymer/LiPo/LiPoly batteries, there are a lot of terms you will need to know before we get started.  Everything may seem a bit daunting at first, but with some basic understanding, it's all pretty simple, so let's jump in.

When you look at a LiPo's data sheet or casing, you will notice it has a lot of specs.

Cell arrangement - Described using the format xSyP (where x and y are integers), this tells you how the cells in the battery are wired up.  Batteries are made up of cells, whose voltage is determined by cell chemistry and whose capacity is determined by energy density and physical size of the cell.  S stands for series and P stands for parallel.  As you may know, series adds the voltage of the cells and parallel adds the capacity of the cells, so a combination of cells in series and parallel results in a battery.  The battery shown in the second image reads that it has an arrangement of 3S1P, meaning it has 3 cells that are all in series with no parallel wiring.  This may seem confusing because it says "1P," but think of the arrangement as a grid.  By multiplying the 3 and the 1, you get the total number of cells in the battery, which in this case is 3.  If it were a 3S2P battery, there would be 2 sets of 3 series-wired cells in parallel, resulting in 6 cells total.  Often times the parallel arrangement is omitted when discussing batteries, because most packs are 1P (so instead of saying you're using a 3S1P pack, you may as well just say 3S).

Capacity - Usually measured in mAh (milliamp hours), this is determined by the cell arrangement (parallel) and tells you how long you can expect the battery to last on a charge (although it's not quite that simple).  2600mAh as shown on the battery in the picture is equal to 2.6Ah (amp hours), a format you may be more familiar with on larger batteries, like the SLA (sealed lead acid) one in your car, which is probably around 50Ah.  A capacity of 2600mAh means that the battery can discharge at 2.6 amps for one hour (hence "amp hours"), 1.3 amps for 2 hours, etc., before it runs out of "juice."  Because the battery shown has a 1P arrangement, each cell has a capacity of 2600mAh.

Voltage -The voltage of a battery is also determined by the cell arrangement (series), and there are a few common voltage measurements worth noting:
        Charged - the voltage of a fully-charged LiPo cell is 4.20V, and charging above this will damage the cell.
        Nominal - this can be considered a sort of "half-charged" voltage, as it is 3.70V, in between charged and discharged.  Nominal voltage is what manufacturers use when describing the voltage of their batteries.
        Discharged - the voltage of a discharged LiPo cell is 3.00V, and discharging below this will definitely damage the cell.
Because the battery shown has a 3S arrangement, it is marked with its nominal voltage of 11.1V (3.70V*3 cells).  A fully charged 3S pack is 12.60V and a fully discharged 3S pack is 9.00V.

Constant C Rating (Discharge) - The constant C rating (in relation to discharge) tells you how many amps can be safely drawn from the battery constantly.  The "C" in a rating of xC (where x is an integer) actually stands for the capacity of the battery in Ah.  By multiplying the C rating's coefficient by the capacity of the battery in Ah, you can determine the sort of amperage you can draw.  In the case of this battery, with a capacity of 2600mAh (2.6Ah) and a C rating of 55C (that's pretty high, FYI), I can multiply 55*2.6 and get the max constant output of my battery, which is 143A.

Burst C Rating (Discharge) - In addition to the constant C rating, there is also a burst C rating, which is higher.  Most of the time, the "burst" is rated for 10 seconds.  Although it is not marked on the battery itself in the picture, it says in the documentation that this battery's 10 second burst rating is 80C.  So, 80*2.6 is 208A burst. That's a lot!  It's worth noting that your LiPo won't last long when that many amps are being drawn from it.  At 208A, a 2600mAh LiPo will last approximately 45 seconds.

C Rating (Charge) - Determined in the same fashion as the C ratings for discharge, the C rating for charge tells you at what amperage you can safely charge your battery.  This information is generally listed on the back of the battery with all the safety information.  For the battery shown, it happens to be 5C, which means that it can be charged at 13A (2.6*5).  We'll be talking a lot more about charge rates later...
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Can anyone please tell me the function of each wire in the battery (Image attached). It's a tablet battery.

Or can anyone direct to a resource that illustrates the wiring of a Lipo battery.

I'd be grateful!

Thanks

~amol

s-l1000.jpg

It is Li-ion battery, not LiPo...

It says Li-Polymer right on the label. That is indeed a LiPo battery.

ColinM11 month ago
ColinM1 ColinM11 month ago

sorry my question didnt show up , so trying again,.

My question is do you ever discharge and charge singularly or a series of cycles after normal use of a Lipo. I`m also dont understand disharging/charging to measure capacity , could you please explain how and why?

mjackson421 month ago

Brilliant Instructable. Thanks very much.

marc brown1 month ago
Thanks for the awesome instructable.
Akin Yildiz1 month ago

thank you for this great post. covering all the basics.. however I have a few questions about the mini lipo batteries for mini quadcopters.

these batteries are usually 3.7V, 240mAh and 25C but can go upto 800mAh

my main question is do you think these usb chargers are okay to use? they are supposed to turn off once it reaches 4.2V - I have been using them heavily the last 2 weeks without problems, but I always set a timer for about 40 minutes and check the voltage with a multimeter at this minute mark. just to be safe. however i did catch one time that the battery was at 4.4V after charged. it looked a bit bloated as well. however i keep using this battery still with extreme care now. and its still going strong.

and can I plug in these mini batteries to a more advanced charger as yours above? i don't think there is a charge rate mentioned on the battery to calculate how fast/slow to charge them. i'm guessing these are all single cells.??

here is a link; http://www.ebay.com/itm/Attop-YD-928-Charger-Batte...

as you can see there are no real info on these batteries anywhere, not even printed on them..

Screenshot 2015-05-21 at 10.54.54 AM.png
SarthakJ1 month ago

Hello there!

What if i have 5200mah 3cell battery? But the charger has max 5.0A( for 1C charge rate) for 11.1(3s). Is it okay to charge the Lipo at 5.0A?

Thank you!
Sarthak

In general, you can charge a pack more slowly with complete safety. It's actually less stressful on the battery pack and will prolong its life, at the expense of increased charge times.

The critical point is to match the charger's charge voltage to the cell you are using. The voltage is what the charger uses to detect the charge state. If the voltage spec of the charger matches the nominal voltage of the battery pack you're probably OK.

Thanks!

VanceB14 months ago

I plan to use a lithium polymer battery to power an Arduino project, but to charge it from a solar cell. I will use a charger such as this one from DFRobot http://www.dfrobot.com/index.php?route=product/product&product_id=1139, but can you advise on whether it is OK to charge the battery on a much lower current than the rated values or will this reduce battery capacity?

JoGusto VanceB11 month ago

Definitely OK to charge using lower current. Just don't exceed the "stop charging me" voltage of 4.2 v. Stopping even earlier (eg, 4v) will prolong the life of the cell and still give you 50-70% (approx) of the total possible charge.

Radioactive_Legos (author)  VanceB13 months ago

Hey there, sorry for the late reply. As far as I know, there aren't any downsides to charging a LiPo with sub-C currents, besides the longer charge time.

patrick.vet.52 months ago

Hey all,

I've got a 7.4v WE 1200mAh 20c LiPo battery for my airsoft rifle, but it wont charge anymore. The charger/balancer keeps telling me "Low Voltage Warning". Also the battery feels a little 'bloated' if you know what I mean. Any tips on how to proceed?
I was going to just throw it out and buy a new one, but I am curious if there is any way to salvage it.

Thanks in advance.

I suspect this battery was charged on the wrong charger, and now it's been overcharged, causing the cell to bloat and plate the electrodes with metallic Lithium. The cell is probably ruined and unsafe to use.

I would make certain that your charger is for 2S configurations, not 3S. A 3S charger will keep shoving current into the battery, trying to get the voltage up... it all kinda makes sense if your charger is warning "low voltage"... it sees 7.4 instead of 11.1 volts, and thinks there's something wrong with the battery.

Sorry to say, by now there is... Chucking it is the right plan. Might want to get a geek to check your charger for you, too.

JoGusto1 month ago

Some things to note about Lithium batteries in general... just to reiterate!

1) if mishandled, they are DANGEROUS. They will explode and catch fire, no joke! Overcharging, overdischarging (too much current/short circuit) etc.. not good. Fortunately, may come with protection circuitry built in (amazing!). I think these RC high-discharge cells possibly would NOT be protected, so be respectful of the danger if mishandled (charged the wrong way, etc).

2) Li-Po describes a method of construction for the cell (polymer electrolyte element). The cells could have Lithium Ion chemistry (lithium-metal) or they could possibly have another chemistry (eg Lithium Iron Phosphate). The chemistry changes the cell voltage! The cell voltage determines which charger must be used! Be certain of your cell NOMINAL voltage, and that it matches what your charger will handle! Charging a Li-Fe-PO4 cell with a Li-Ion charger will damage or explode the cell, or cause a fire, quite possibly, and will almost definitely ruin the cell via overcharging.

3) The best way to prolong the life of your Lithium cell is to not overcharge it, or try to "top it off" to the max charge voltage. This last 20% of the cell capacity stresses the cell due to the high voltage, and significantly reduces the service life of the battery. Most products want that full charge, so they can tout total standby or operating hours per full charge, but that kills the cell before its time.

You can really extend the cell's life by only charging it to the constant current cutoff point, where the charger switches into constant-voltage mode, or even a little before that point. This can extend the life of the cell 3 to 5 times over the usual "top off" charge, but of course, at the expense of less charge stored meaning less run time for the battery during use. It's also better to drain the cell pretty well before charging it again, rather than trying to top it off every time, even if only slightly discharged. Once again, this is to avoid the high charging voltage regime, where the battery gets stressed.

If you want to store a cell, the recommendation is to charge it to about 40% capacity before putting it on the shelf.

Hope this helps!

jhsa1404671 month ago

Great instructable.

I think it's worth saying that a Lipo cell should not be Discharged under 3.0V UNDER LOAD.

At rest the battery might be over 3V per cell but if you put some load on it it might go under quickly if it is discharged, or if the appliance take too much current. The higher the current, the higher the voltage drop. And that is how people ruin the batteries sometimes specially when using them for radio control . Also when used on low current setups, the voltage threshold should be set higher. For example on a radio control transmitter the current consumption is very low, meaning that the voltage drop is also very low. If you set an alarm too low, the battery will be completely discharged but the voltage will still be above the low voltage alarm setting for a while, and then it will suddenly drop, leaving you no time to do anything before your appliance turns off and the battery probably gets destroyed. In low current setups it is wise setting the alarm/cutoff at 3,7V per cell. This setting will leave the battery with around 20% of it's capacity, which I think it is recommended. I hope this comment is useful to someone..

BAURO1 month ago

is it possible to charge a 12v lipo without connecting the balance lead to the charger?

I have a 12v 3S lipo and I want to charge it without the balance lead connected cause I want to put it inside my speaker and the lead is too short.

Radioactive_Legos (author)  BAURO1 month ago
You can charge a LiPo without connecting the balance leads, but you won't be able to balance charge it. Balance charging is typically recommended so your cells don't drift apart in voltage over time. I'd recommend purchasing an extension for your balance leads - they're typically terminated with JST connectors, which are pretty standard and easy to find.

Thanks for the help

AnatolyG12 months ago

To answer some questions:

What to do to make your battery last longer?

- keep it cool at all times;

- don't charge it fully. Battery charged to 4.2V has only 10% more charge than when charged to 4.0V, but voltages over 4.0V greatly accelerate battery deterioration;

- keep charge and discharge currents as low as possible.

How long can a LiPO battery last?

-under favorable conditions (see above), battery's capacity will decrease to 1/2 in 15 years.

Can I charge a battery at lower than 1C current?

-yes, the lower the better.

Do I really need a specialized charger?

no. A battery can be manually charged using a regulated power supply with controlled voltage and current. First charge at constant current until voltage reaches 4.2V/cell, then step down to 1/2 current followed by 1/4 and 1/8 current, while monitoring cell voltages. Make sure battery stays cool. If perceptible warming occurs, reduce charging current or stop charging until temperature returns to normal. If the battery is charged to 4.0V/cell, balancing is not necessary. Needless to say that you cannot leave a charging battery unattended.

Can a dead LiPO battery be revived?

-it depends. Cells having low voltage (1-3V) can usually be revived with some loss of capacity. Completely dead cells (0V) can often be restored to 1/2 of their original capacity.

How to revive a dead battery?

Li ion automatic charger will not charge batteries with less than 3.0V/cell. If the voltage is lower, start charging a cell or a string of cells manually at 0.1A constant current for 10 min, then disconnect charger and check cell voltages. Those lower than 3.0V are bad. Those higher than 3V may be usable. Charge them at 0.5C and check their temperature. Those perceptibly warming are bad. Continue charging the cool ones as you would do with good batteries. If they can be charged to 4.2V without warming, they are OK. If they start warming towards the end of charging, they are bad.

tomic2 months ago

thanks for the succinct writeup! i've been putting off dealing with LiPo's for as long as i could! but now i'm back to super low power controller stuff and needing to contemporize. thanks!

BrentB13 months ago

Excellent write up - Thanks!

MatteoF14 months ago

It's a great guide, I suggest you may add:

- "reviving" undercharged LiPos (as this guy did:http://electricrcaircraftguy.blogspot.it/2014/10/r... ) It's a dangerous procedure but it works good!

- charging more than one LiPo at the time, for example 2 x 3S 4500mAh can be charged by putting them in SERIES (with an adaptor for the "main",red and black, and single cell cables) and setting the charger to 6S, with 1C (4.5A) charging current.

Cheers

It would be great if you could add a section on "conditioning" a new battery for best performance. I know that charging and discharging is how you do it, but not the specifics for best results.

DavidT105 months ago

Hi there!

Other than the obviously high cost, what do you think about using a small, say 3.7v/1200mah in a Solar/PV charged LED lamp as opposed to Nimh batteries?

Thanks,

Dave

Hi.

I have a 4S 8000mAh LiPo battery from Hobbyking and i'd like to
integrate it in a system where the battery would be powering a load (up
to 80A discharging, typical 40A) and i'd like to charge the 4S LiPo
battery while the system is working. Is it possible? I wanted to have
the charging board inside my system. I justed wanted a DC cable to plug
and charge the system (even when in use).



I found things like this: http://www.batterysupports.com/12v-1...tem-p-245.html



But i don't know if this is what i need for charging or if this is just a protection.

hi and thanks for the great instructable! I wanted to know if you could charge and discharge from a lipo battery at the same time? I have heard that it isn't recommended, but is it possible to do it taking necessary precautions?

And if it isn't, will this be possible with li ion batteries?

NRG4UandMe6 months ago

thanks for the nice explanation of tech terms on a lipo which I am still learning about !

MomenIbrahem11 months ago

I have had a problem with my LIPo battery it's working and its 3 pack voltage is 1.39 volts , btw it dropped suddenly from 9 volts to this voltage (2200 mA 3s1p )
my charger is not charging to when connecting the balanced charging pins too

Does this means that it has been damaged ?

Radioactive_Legos (author)  MomenIbrahem11 months ago

I would advise against trying to save that battery. It's worth checking the voltage of each cell by measuring from the common ground on the balance tap to each of the other wires. I'm curious as to whether or not all the cells drained evenly or if one or two are dead entirely. LiPos have a different discharge curve from most batteries because they drop some voltage at initial discharge, remain near their nominal voltage for most of their capacity, then drop off voltage very rapidly at the end of their discharge cycle. Check out this graph to see what I'm talking about.. As you can see, it's very easy to over-discharge a LiPo if you don't stop using it in a timely fashion.

Capture-2.PNG

It also appears (from your chart) that charging beyond 3.8V at room temperature (20C) is nearly useless because you gain less than 300mA from 3.6 to 3.8V.

I'm not convinced your chart is accurate though... it also indicates that the max. charge is 3.8V at room temp, yet I routinely charge lipos and standard lithium ion cells (same chemistry I believe) to 4.2V even at room temp, and both my Accucell and Nitecore chargers show that it puts a substantial charge on from 4.1 to 4.2V.

Radioactive_Legos (author)  JB166 months ago

I think you may be interpreting the graph incorrectly. It's a discharge graph and it says at the top that the battery was charged to 4.2V. I believe the reason the 25C discharge curve begins at 3.8V is simply due to the voltage drop from the large load (drawing 105A). You can see that when the load is small with a 1C draw from the battery (4.2A), the battery's voltage does not drop much, and is much closer to 4.2V.

HansBaumann10 months ago

Hello,

I am wondering if anyone can tell me if I am going in the right direction here:

Item:
lipo battery 551419 3.7v
75mah lithium li-polymer
battery for rc helicopter

We want to use this battery for a back up system as follows:
1. We have 24VDC that are usually running our device (a valve actuator)
2. When the power supply fails, we need about 20-22V @ 2A for 0.5 seconds and then @ 1A for about 5-10 seconds
3. The power supply will fail less than once every month
4. What is your recommendation to keep this battery pack connected to the charger (6 cells in series), so that it can perform this service the longest time possible?
5. The battery does not need to be good for longer than 10 minutes after power failure of the supply

My reading so far suggests that for the best batter life I would have to do the following:

Since LiPo battery life is counted in "cycles" and temperature, I think that charging when it goes to 3.6 and only up to 3.7V would be best.

I would like to know if anyone has experience with something like that and particularly, if its reasonable to believe that a battery pack built based on this outline wile have a good chance of surviving for 4-5 years.

JB16 HansBaumann6 months ago

It sounds like you could get by nicely with three 9-volt alkaline cells connected in series. These would be non-rechargeable, but it sounds like with your small monthly current draw they may last for the actual storage life of the batteries.

Certainly the heli battery (3.7V, .075AH) would also be sufficient (connecting 6 in series, or "6S"), but massive overkill. You need 1A for 10s, 2A for .5s:That's 11 Amp-seconds, or about (11/60) Amp-minutes, or .003 Amp-hours, or 3mA-Hrs, which would be enough for about 25 of these cycles. Depending on the self-discharge, you could safely charge it manually once a year! Since a typical 9V alkaline has over 500mAh of capacity, your 3S 9V battery pack would theoretically last 170 cycles. Assuming this to be a monthly occurrence that's over 12 years!

Great guide! Really helpful! Just a couple of questions though, will the charger automatically balance the cells, or would I have to set it up? Also, Alot of people say to discharge/charge my battery to a certain voltage when not in use. What would this voltage be? I have a 7.4V (3.7V per cell) 2s 5000mah LiPo. Thanks!

Thanks! The answers to your questions are actually in the Instructable, but I'll answer them separately here for clarity. If you have a balancing charger, it will automatically balance the cells if you charge the battery in balance mode with the balance tap connected. As for the voltage people are talking about, that's covered in Step 7: Storage. 3.85V per cell should do the trick. Hope this helps!

Thank you very much. But wait, what does 3.7 V per cell stand for on my battery? If it can go higher..

3.7V is the nominal voltage of the battery, you can think of it as an average voltage during discharge. For more info, check out Step 1: Terminology, under "Voltage"

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