Ways to re-charge a lipo battery after it drops below 2.7v

You need to look at this graph again:
http://neptronix.org/forumpics/lipotutorial/24_dischargingmechanics.gif

Lipo is different from other battery chemistries you might be familiar with. The discharge curve has a VERY pronounced drop off at a relatively high value. Only around the middle of the discharge curve is it even close to linear. You can't calculate your range with a "volts/mile" conversion with any accuracy at all except around the middle of the discharge curve. Even then, it is a strong function of the discharge rate and would only be any use at all for the same discharge rate. It is certainly no good after about 3.7 v/cell or so. After that, your battery capacity is nearly all done. If you keep draining it, it will go over the cliff in the graph. If you want to know how much capacity you have used, you need to monitor the watt-hours of use since charging. Even then, it is only an approximation and will depend on the discharge rate. The low voltage cut-off is to protect your battery, not to predict range.

Damage to RC Lipo is not reversible. Once the electrodes are damaged, they are damaged for good. You will only exacerbate the damage by continued use. Just because it will charge, it does not mean it is rescued. Check the capacity. If it is significantly reduced, get rid of it. I have a pile of burned metal that used to be a $200 controller and some scorched vinyl siding to testify to this conclusion.

I've pretty much just re-iterated the previous postings, but there you are.

Edit: See the following for examples of different battery chemistries:
http://homepages.which.net/~paul.hills/Batteries/discharge.gif

This are idealized curves and Lipo is not on there, but you get the idea.

See, what confuses me here is that you guys are giving contradictory info. Over. and over. and over.

Ive been on this forum on and off for maybe a year or so. (Much more actively in the past few months than before that.) Every single time Ive visited the forum, I see "The golden rule of lipo" and "Never below 2.7" EVERYWHERE. Many of you have it in THIS very thread, whether in your signatures or in a post or whatever. I doubt you could browse a single thread on here without seeing "the golden rule is sacred! obey the golden rule! 2.7 and 4.3! TWO POINT SEVEN! FOUR POINT THREEE! TWOOO POOIIINT SEEEVVVVEEEEEENNNNNNNNN!!!!" (forgive the theatrics, but you get my point. Its posted everywhere.)

And yet now, here we are in this thread, and suddenly, all I see from people is;
"Why would you EVER think you could go to 2.7?!"
"You CANNOT ride to 2.7!"
"How can you POSSIBLY not know that 3.3 is the minimum?"
"NO ONE rides all the way down to anywhere NEAR 2.7!"
"Ignore the fact that literally everyone here has previously told you the golden rule is 2.7 minimum, NOW we're gonna tell you its 3.3 mimimum!"


I think you can see where my confusion comes from. Basically, I find myself compelled to ask; If you should never go below 3.3... THEN WHY HAS LITERALLY EVERY MEMBER OF THIS FORUM BEEN SAYING THAT ITS 2.7?!

I apologize for the rudeness, but seriously. Thats ridiculous. How are you going to have it plastered all over the forum that 2.7 is the minimum, and then just suddenly have everyone change their minds and say that 3.3 is the minimum?
Which is it? Why would you ever even SAY it was 2.7 (much less put it in your signitures) it its really 3.3?

You have to understand that to a newbie, coming to this forum and seeing "The golden rule of lipo; never below 2.7, never above 4.3" posted EVERYWHERE, that person is going to believe (as they logically should) that they can safely drain cells down to about 2.7, maybe 2.9 to be safe, with NO negative repercussions.

Posting 2.7 everywhere will invariably lead to people thinking its ok to discharge down to 2.7.

Even if its posted or clarified elsewhere that 2.7 is the absolute minimum and 3.3 is the USEFUL minimum, you still have to understand that it is VERY misleading to have 2.7 posted in literally every single thread, and 3.3 posted.... nowhere. I have been coming here a few times a week for the last few months, and I have NEVER even once seen anyone say anything about 3.3 before this thread.

On the other hand, I have seen hundreds of people/posts/signatures saying that 2.7 is the minimum.



Be realistic; what conclusion am I expected to reach? I see 2.7 posted everywhere I look, and not one single mention of 3.3, or even a single post (before this thread) giving ANY indication that I shouldnt go down to 2.7.
I see 2.7 on every single page, so I believe that I can go down to 2.7 safely because that is what I am told.


You cannot tell someone over and over and over that they can take their cells down to 2.7, but no lower, and then freak out at them when they do! If the REAL minimum is 3.3, then hey, here's an idea; why not put that in your signatures and posts and FAQs and noob threads so that people dont get the wrong information.

I really do apologize for my somewhat blunt language, but I think you can understand my frustration. Imagine going to school and being told by every single student and teacher that lunch is noon in room 221, only to get to room 221 at noon and find no one there, and then get detention for not magically knowing that it was actually at 11:30 in room 488.

omegagamer89 said:

See, what confuses me here is that you guys are giving contradictory info. Over. and over. and over.
...rest deleted for space

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+1. The guy has a point.

Practically speaking though, in terms of a low voltage cutoff, the difference between, say 3.6 and 2.7 is about 10 feet of road. At some point your battery is going to go over the cliff and at 3.7, you are very close to being there.

In this case, you are already there so the rule of thumb is academic at this point. If you got down to 2.7v and did not continue to let it discharge and charged pretty soon after that, you are probably fine. The fact is that there are few people who actually know what voltage and what time EXACTLY is a problem. What number and what time you use is pretty much a function of how much safety factor you want. Lithium would work best if you drive to the end of your driveway and recharge. It works the worst if you drain it to zero. Somewhere in the middle you go from simply discharged to dangerously damaged. Pick your point, but I'd say most people here are simply speculating based on experience. The 2.7 number is an often quoted one. Not sure if there is basis in testing data or not. It probably varies based on time the battery sits at that state and the discharge rate at which it reached that state. The fact that your charger did not recognize your battery indicates at least it thought you had gone too far.

Charge outside.

pdf said:

+1. The guy has a point.

Practically speaking though, in terms of a low voltage cutoff, the difference between, say 3.6 and 2.7 is about 10 feet of road. At some point your battery is going to go over the cliff and at 3.7, you are very close to being there.

Click to expand...

Thank you. I just wish that had been better explained before I potentially ruined a pack. If I may, I would ask that people who have the 2.7 rule in their signature edit their signature so as to make the difference between the 2.7 "minimum" and the 3.3/3.6/3.7 "minimum" more apparent.

As things are now, with HUNDREDS of signatures all over the forum saying 2.7 is the minimum, there WILL be other cases like mine. Its not a matter of IF, its a matter of WHEN. Having the whole golden rule, 2.7 spiel in 90% of signatures will invariably lead more newbies into destroying their packs.

I respectfully ask that if you have the '2.7 minimum" or anything similar in your signature, you edit it in some way to make it clear that riding down to 2.7 is not a good idea. Perhaps something along the lines of " THE GOLDEN RULES OF LIPO: Never above 4.3v, Never below 2.7, stop discharging at 3.6v, never puncture! would make things more clear to those of us who are just starting.


EDIT: I just noticed neptronix already has/had something like this in his/her signature. Whether it was already like that, or was changed in response to this thread, I thank you. Your signature will hopefully help prevent another from making my mistake. Cheers!

The 2.7V is roughly the point where you may have damaged the cell so much that it shouldn't be used in normal operation. Of course this can vary from cell to cell, but the point is you should never really go below the point where you have used all 100% of the soc. That happens at about 3.3V. Once below ~3.6V cells tend to start going way out of balance. Yep, I griped about the 2.7V/4.3V thing in someones sig for some time before he added the normal operation voltages. There's just no point in going below 3.6V per cell if you don't want to get your pack out of balance too much. I run 24s, and have my LVC set to ~88V (3.67V per cell. If I run it down to the point LVC cuts me off, I've still got a 10% SOC and close to 3.7V per cell resting voltage. Setting LVC to 3.5V per cell will pretty much guarantee you've never go below 3% soc. Going lower than that by much will pretty much guarantee you're damaging your pack and shortening it life span. As for the top end, you shouldn't charge over 4.2V per cell, although I've gone as high as 4.23V without any apparent damage. Look through this thread and come to your own conclusions.
http://endless-sphere.com/forums/viewtopic.php?f=14&t=47294

If the sum total of a persons research into RC lico batteries is reading my signature, then that person will be spending some money learning things the hard way.

And, they didn't read the second line. Which another member wisely suggested I add.

dogman said:

If the sum total of a persons research into RC lico batteries is reading my signature, then that person will be spending some money learning things the hard way.

And, they didn't read the second line. Which another member wisely suggested I add.

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That's why I asked the question with respect to his choice on using LiPo and how he came to that decision.

omegagamer89 said:

See, what confuses me here is that you guys are giving contradictory info. Over. and over. and over.

You cannot tell someone over and over and over that they can take their cells down to 2.7, but no lower, and then freak out at them when they do! If the REAL minimum is 3.3, then hey, here's an idea; why not put that in your signatures and posts and FAQs and noob threads so that people dont get the wrong information..

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My friend,... this is not a classroom,..its a public forum with anyones opinion and interpretation ( right and wrong) posted for the readers information. Its YOUR responsibility to read and filter and interpret that information before taking actions.
You didnt read/ research all the available info before you chose to use your packs.
You didnt charge your packs before use.
You didnt understand the critical discharge characteristics of your packs. ( and still do not from your last posts !)
and i dont believe you understand the risks of what you are doing.

Dont blame the forum for your mistakes !

omegagamer89 said:

As for the people saying it was dumb to ride with only 3.8v per cell, I fail to see how. 3.8 is not "almost empty." In fact, 3.8 is much closer to full than it is to the minimum discharge.
If the max charge per cell is 4.3v, then 3.8v is only .5v away from full. Whereas its 1.1v away from 'empty' (AKA 2.7) I mean, sure, 3.8v isnt full, but its also nowhere near the 2.7v cutoff. I mean, if I had started riding with, like, 3.0v per cell, then yeah, thats pretty dopey. But if 2.7 is 'empty' (AKA 0%) and 4.3 is full (AKA 100%, then that means 3.8 would be close to approximately 70% full.

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No. Instead of going by how you think it should work, and please read Lipo Basics. http://www.rcgroups.com/forums/showthread.php?t=209187 The graph already posted should have made it obvious; maybe this will help. Please notice how a 10% drop in voltage = 80% capacity used.



I'm sorry this is frustrating. Certainly don't want this to seem like an attack but more than that don't want you burn your house. Frankly, I think the never above 4.3 is misleading.. That absolute maximum voltage of Li is something like 4.22? and 4.2 is 99.9% charged anyway.

So now you know. Balance charge to 4.2, discharge under load to 3.5 (you can use more conservative #s for longer life), store at 3.8. Never charge unattended, store in a safe place. here's great info related to lipo failures: http://www.mpoweruk.com/lithium_failures.htm

Btw, a new battery discharged to 2.x volts under light load and recharged immediately is probably ok BUT the reason this is not suggested is.. a novice won't understand why an older battery left discharged at 1.9 for a week is much less stable and could ignite if charged, So it's safer to say: trash it.

Some of the confusion may stem from how your voltage measurements are being made. If you're draing the pack at 10C and you hit 2.7v, then immediately stop draining the pack, the voltage will bounce back up above 3.0v. Due to the increased cell resistance at lower voltages, the voltage sag will be exaggerated.

This is why most lithium battery protection systems have a rather low cutoff voltage.

omegagamer89 said:

And yet now, here we are in this thread, and suddenly, all I see from people is;
"Why would you EVER think you could go to 2.7?!"
"How can you POSSIBLY not know that 3.3 is the minimum?"
....
THEN WHY HAS LITERALLY EVERY MEMBER OF THIS FORUM BEEN SAYING THAT ITS 2.7?!

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Not suddenly. This is not new information, it isn't a secret. It is all here on the ES forum. If this is new information to you then YOU haven't done enough research. There are thousands of posts here saying lipo isn't for noobs, repeating ad nauseam that it requires your doing research, warnings and what not. There are many hundreds of threads on how to run lipo packs, discharge graphs, voltages etc.

omegagamer89 said:

I just wish that had been better explained before I potentially ruined a pack.

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Seriously? Do you expect a mod to contact you and walk you through it personally?
Remember that it's your responsibility to read and understand these threads and if in doubt ask for advice and you'll be fine. As you can already see from this thread there is no shortage of people willing to help.

the insiders have nothing to do with it. it is defined in the literature that a fully discharged lipo pack at resting voltage is at 2.7V. fully charged, resting voltage is 4.2V and if you raise the cell voltage above 4.3V then there is the risk of fire starting from overcharging. this is all in the literature. i have even read that 4.356V is the specific voltage that causes them to ignite. but i have seen lipo packs at 4.5V and not burning. puffed, but not burning.

On the product page, i believe that hobbyking states a minimum voltage of 3.0v.



Nonetheless, there is very little capacity past 3.5v. It's not worth dipping lower than that.

Gregory said:

Not suddenly. This is not new information, it isn't a secret. It is all here on the ES forum. If this is new information to you then YOU haven't done enough research. There are thousands of posts here saying lipo isn't for noobs, repeating ad nauseam that it requires your doing research, warnings and what not. There are many hundreds of threads on how to run lipo packs, discharge graphs, voltages etc.

Seriously? Do you expect a mod to contact you and walk you through it personally?
Remember that it's your responsibility to read and understand these threads and if in doubt ask for advice and you'll be fine. As you can already see from this thread there is no shortage of people willing to help.

Click to expand...

I have read through all the noob threads, info threads, FAQ threads, battery info threads, and this is the VERY first time anyone has EVER mentioned 3.3v instead of 2.7, so yes, it is sudden. If I can read through a dozen threads about the subject, and not see anyone say anything about 3.3, while seeing TONS of mentions of 2.7, then there is a problem. How was I supposed to know this? Where was I suppsosed to get this info from? I LOOKED. I did the research, I tried to find the info. And know what? EVery single time, all I came up with was people saying 2.7 was the limit, not ONCE did anyone say anything different.

As for the second part of your post, no, I dont expect anyone to message me personally to explain. What i expect is that the correct information is OUT there and readily available. Look through all the newb threads. Go ahead, do it now. How many instances of statements to the effect of "2.7 is the minimum" do you see? A LOT. Now, how many isntances of "3.3/3.5/3.6 is the minimum" do you see? None.


The bottom line is this: If someone comes to this forum looking for info, and sees HUNDREDS of posts saying 2.7 is the minimum, then they are going to believe that 2.7 is the minimum, and that they can safely discharge their packs down to 2.7, and that they will be fine as long as they dont go below 2.7.


Yes, I was ignorant of the fact that voltage loss isnt linear like it is with other things, but that is a separate issue from the overabundance of "2.7 is the minimum" posts and the complete and total lack of "you shouldnt go below 3.3" posts.

Hi,
There is an excellent page on the wiki Batteries_LiPo

But I do agree it is very hard for a noob who doesn't have the knowledge & search skills (eg use the google search), so I hear your frustration omegagamer.


Seriously the best solution I see, once you're on the road again I hope you can collate all this learning and get it stickied, or come back and assist noobs threads (like dogman, neptronix, wesnewell, spinningmagnets and dozens others do daily), or update the wiki where required. No one gets paid to do this work, and you're just as smart as anyone.
Do not expect someone else to do it and then complain when they don't.

Hope you get your bike up and running soon.

dnmun said:

the insiders have nothing to do with it. it is defined in the literature that a fully discharged lipo pack at resting voltage is at 2.7V.

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Anyone that listens to this BS will end up with a dead pack prematurely, if not a ball of fire. Why this person keeps writing this crap is beyond me. He has very little experience with rc lipo and I've never seen any docs from him that supports these absurd statements, and never will, because they do not exist. OTOH, there's many charts, graphs, photos, etc., that do show the real SOC at various voltages.

4.3v max 2.7v minimum is the range where you can have a reasonable expectation that your battery will not catch fire. It's NOT a good idea, in ANY chemistry to practice 100% discharges.

This is stated quite clearly in the thread in Battery FAQ's, Lipo Battery Care and Basic Information. On page one. That's why the link to that thread is there in Battery FAQ;s sticky thread. http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=9170&start=0

I certainly never advised anyone to discharge all the way 2.7v. My advice, as stated a 24,000 times in the sig of every post including ancient ones, is to stop at about 3.65v. Quite conservative actually.

Sorry you missed that. I don't know how many threads that graph showing the discharge curve has been posted in, but its' pretty hard to miss too.

But hey, shake it off. I did stuff very similar the first two weeks I had lico. I just didn't appreciate that the beeper did not mean a mile to go, but rather a block. I thought the exact same thing, that 3.5v is a long way from 2.7v, so I can make it home. Its not, and I learned that very fast. Those first packs I learned the hard way, and they were gonners in less than a year. I rode em hard, and put em away wet, and they lost capacity fast. Now I practice a much easier use pattern and hope for 2-3 years.

Just go buy some more, and call it lesson learned.

"The voltage of a Li-poly cell varies from about 2.7 V (discharged) to about 4.23 V (fully charged), and Li-poly cells have to be protected from overcharge by limiting the applied voltage to no more than 4.235 V per cell used in a series combination."

"All Li-Ion cells expand at high levels of state of charge (SOC); if uncontained, this may result in delamination, and reduction of reliability and cycle life; the case of cylindrical cells provides that containment, while pouch cells, by themselves, are not contained. Therefore, to achieve the rated performance, a battery composed of pouch cells must include a strong external casing to retain its shape.
Overcharging a Li-poly battery can cause an explosion or fire.
During discharge on load, the load has to be removed as soon as the voltage drops below approximately 3.0 V per cell (used in a series combination), or else the battery will subsequently no longer accept a full charge and may experience problems holding voltage under load. Li-poly batteries can be protected by circuitry that prevents over-charge and deep-discharge.
Compared to the lithium-ion battery, Li-poly is less advantageous in terms of life cycle degradation rate.
Lithium polymer-specific chargers are required in order to avoid fire and explosion.
Explosions can also occur if the battery is short-circuited, as tremendous current passes through the cell in an instant. Radio-control enthusiasts take special precautions to ensure their battery leads are properly connected and insulated. Furthermore fires can occur if the cell or pack is punctured.[14]
While charging the lithium polymer batteries, the individual cells in the pack should be charged evenly. For this purpose, the cells are to be charged with special chargers. This entails special care while charging the batteries in addition to incurring expenses on procuring the chargers specific to lithium polymer batteries."

"LiPoly batteries must be charged carefully. The basic process is to charge at constant current until each cell reaches 4.2 V. The charger must then switch to a constant voltage mode, and the charging current will gradually reduce while the charger holds the cell voltage at 4.2 V. This will continue until the charge current has dropped to a small percentage of the initial charge rate, at which point the battery is considered fully charged. Some manufacturers specify 2%, others 3%, but other values are also possible. The difference in achieved capacity is minute.
Balance charging simply means that the charger monitors the voltage of each cell in a pack and varies the charge on a per-cell basis so that all cells are brought to the same voltage.
Trickle charging is not recommended for lithium batteries.[15] Most manufacturers claim a maximum and minimum voltage of 4.23 and 3.0 volts per cell, respectively. Taking any cell outside these limits can reduce the cell's capacity and ability to deliver full rated current.
Most dedicated lithium polymer chargers use a charge timer for safety; this cuts the charge after a predefined time (typically 90 minutes).
As of the beginning of 2013, charging rates of up to 15C (i.e., 15 times the capacity of the battery, or approximately 4-minute charge times) are possible in the relatively new (circa 2009) breed of nanowire technology LiPo batteries. This, however, is the exception to the rule, as the more common 1C charge rate still stands as the recommended standard among RC users. It is also important to note that regardless of the charge rate that a battery can handle, using the lower 1C charge rate will always increase the longevity of any RC LiPo battery."

i would like for wes to provide the same documentation of his statements.

omegagamer89 said:

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One member posted this picture its PERF*

My brother is the same age as you and was stuck with ebikes after I let him try my bike. So I fixed everything and bought and even told him thirty three times how to charge his lipo batteries and be very cautious while doing so and be safe and watch them while charging. So he used his bike a day and I just decided to come by and look to his batteries if they were alright. Yeah, they were alright ONLY charged to 175% of normal!!! So I screamed at him how dangerous it was and I also got him a charger were he cannot setup the charger wrong.

I did same thing as you on a ride but I did understand that I had very little battery left and I had to walk my bike 4 miles home. My setup was powerful and drained my batteries in seconds meaning the cells in my lipos fell from 3,8V to 3V very fast, even one was down to 2V and two cells at 2,7V. It happened over a one mile ride. Those batteries are OK now and I use them.

My charge limit on each cell on rare occasions is 4.20V Use 4.1V regularly and 4.15V often.
My discharge limit on each cell is about 3.5V but I try to have as high value as possible. I often get 3.75V and 3.65V after a ride.

Because you use a higher voltage than the controller low voltage is set for it would be wise to have one of these:
http://www.hobbyking.com/hobbyking/store/__10952__Cell_Log_8M_Cell_Voltage_Monitor_2_8S_Lipo.html


I was scared one year ago about lipos but I am not now because I today know their good and bad sides.

dnmun said:

i would like for wes to provide the same documentation of his statements.

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I provide more than just words. I provided photos in this thread showing the resting voltage and 3% soc at 3.5V per cell. At 3.6V per cell, it was 7% soc, and at 3.7V it was 10%. It went to 0% SOC at 3.32V per cell, recorded both on my Hyperion charger and on the power analyzer. So yes, there's 0% SOC at 2.7V, just as there is at every other voltage up to ~3.3V. I choose to believe my own eyes and test over your bs statements. Even rc guys that pull huge C rates from their packs don't recommend setting LVC below 3.0V. On an ebike that only pulls 3-5C, 3.5V per cell LVC is as low as I'd go. Mine is actually at 3.67V per cell, and is at 9-10% soc when it cuts out. With LVC set to 3.5V per cell, it will cut out with ~4% soc.
So you people can believe dnmun or your own eys in this thread.
http://endless-sphere.com/forums/viewtopic.php?f=14&t=47294

so you cannot document your statements and instead insult people who do. of course you will get rewarded by the insiders for deliberately making things up.

dnmun said:

so you cannot document your statements and instead insult people who do. of course you will get rewarded by the insiders for deliberately making things up.

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Are you fricking blind as well. It's documented all over the fricking forum. I'm sorry if this offends you, but anyone that advocates running rc lipo down to 2.7V is just ignorant. I just discharged a spare 4s pack down to 0% soc. when I get time to take a picture of it, I'll post it.

While both are cobalt oxide based chemistry, the discharge profile of a high C-rate RC LiPo cell looks radically different from a high capacity laptop cell or phone battery discharge curve.

I don't discharge RC LiPo past 3.6v, because it just falls off the cliff from there, impedance grows radically and high discharge rates at that SOC result in rapid puffing.

On my cell phone battery of the same chemistry, 3.6v means I've got about 40% capacity left. On an RC pack it means empty.

This is also why the measured nominal voltage of a high C-rate RC cell is typically around ~3.9v, while my cell phone's nominal voltage is ~3.6v.

When your RC pack is sitting at 3.7v, you need to charge not ride.

Exactly. why do the people quoting 2.7v not make a distinction from "lithium cobalt oxide cathode/graphite anode" and other types? My guess is they don't know the difference. Even manufacturer graphs that do go to 2.75 show the mah gained is single digits. While copper plating (and the short/fire risk) is closer to 2v, cycle life is reduced at much higher levels. Same for going above 4.2.

Dnmun, you realize your own link says this:

dnmun said:

During discharge on load, the load has to be removed as soon as the voltage drops below approximately 3.0 V per cell (used in a series combination), or else the battery will subsequently no longer accept a full charge and may experience problems holding voltage under load.

:Most manufacturers claim a maximum and minimum voltage of 4.23 and 3.0 volts per cell, respectively. Taking any cell outside these limits can reduce the cell's capacity and ability to deliver full rated current.:

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Btw, wikipedia is an unreliable source. If you want to learn and cite something useful, cite the datasheets and lab studies the incomplete summaries came from.

Seriously, the 2.7 to 4.3volt comments need to be erased from history. It applies to lab conditions at C/20-C/100 rates and does harm to anyone applying them to real world use (i.e. this forum). 3.5+ to 4.2- is the safe and useful range, so WRITE THAT IN ALL CAPS and delete the rest.

http://www.google.com/url?sa=t&rct=...7YDgDg&usg=AFQjCNFzT1SrZLjbaDQKTzzrX7arrUOVGQ

http://endless-sphere.com/forums/viewtopic.php?f=14&t=54202&p=807447

Even 4.2v is excessively high for the quality/purity of solvents used in RC cells to be sitting around at without having gas production from electrolysis breakdown. I personally run RC LiPo with a 4.1-4.15v HVC for that reason, however, if I'm going to be racing or something, I will charge to 4.3-4.35v if the race distance has the potential to be pushing the packs capacity.