# 3.6 or 3.7 Volts: Why Do 18650 li ion batteries Differ ??



## z_Eftegarie (Jan 22, 2011)

*Hi all, happy I found this place :wave: Some questions in my workflow:*

















*1] VOLTAGE: 3.6V or 3.7V* - 18650 Li Ion Batteries

Are all 18650 lithium ion battery cells 3.6 or 3.7 volts or do they differ?

I want to replace my current SIGMA DP2 photocamera battery (3.7 1300mAh) with a 18650 2900 mAh battery, sometimes rated 3.6V sometimes 3.7V. (I am not sure whether information provided on ebay is accurate as I have seen conflicting data.)



*2] Possible Voltage Shortage?*

Does it matter for my project or can i use 3.6 without any Voltage shortage for the camera? In other words, do all 3.6/3.7V li ions use the same way therefore the given voltage is just the same or do they really differ?



*3] Fundemental Reason for this Voltage Range*

Why do we see only 3.6/3.7 V per Li Ion Cell, and never 3.0V or 4 V per cell?

I am very curious...



*4] Parallel Cell Soldering = best homemade Li Ion Battery Pack*

I was thinking of putting two, or three of those Panasonic/Sanyo 18650 Li Ion cells in parallel, soldering together from the instant the are new, that way giving me about 5800 mAh (2 pcs x 46 grams = 92 grams) or about 8700 mAh (3 pcs x 46 = 1 grams) very light. equalling to bypassing seven orso charges with my old li ion battery. Is this correct?



*5] Charging... How?*

I found a nice small cheap charger about 30~40$ called Turnigy Accucel-6 (there is also an Accucel-8 for double price and double weight) . Could I attach the + to + of all the cells and the - to all the - poles of the cells without needing any extra in-between-wiring? 



Thanks alot for your opinion.


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## PCH (Jul 9, 2015)

I have been wondering about if there's any difference my self thought this thread was the answer. Why are some rated 3.6 volts others at 3.7 volts sorry for the daft questions but I'm just getting into flash light's


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## StorminMatt (Jul 9, 2015)

I know that some Xtar chargers have a 3.6V and 3.7V setting, the SP1 actually has a 3.6V, 3.7V, and 3.8V setting. Basically, the 3.6V is for LiFePO4, the 3.7V is for normal 4.2V (fully charged) Li-Ion, and the 3.8V is for 4.35V (fully charged) Li-Ion batteries. This is admittedly somewhat misleading, since the 3.6V for LiFePO4 is fully charged voltage (vs nominal voltage for the others). They should either make the 3.6V 3.2V instead, or change 3.7V to 4.2V and 3.8V to 4.35V. But this is how they do it. I would look into things more before taking the 3.6V setting for granted as LiFePO4.


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## radu191289 (Jul 10, 2015)

I don't get it either. I bought a 2nd Olight 18650 yesterday (right) and look at the difference between the new one and the one I had from 2014


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## Mr Floppy (Jul 10, 2015)

PCH said:


> I have been wondering about if there's any difference my self thought this thread was the answer. Why are some rated 3.6 volts others at 3.7 volts sorry for the daft questions but I'm just getting into flash light's



Whoa, big thread revival.

The difference is 3.6V is lithium cobalt, the 3.7V is lithium manganese. On the above mentioned turnigy hobby charger, there will be a LiCo setting and a LiPo setting. Respectively 3.6V and 3.7V. The difference there is the LiCo setting will charge to 4.1V and the LiPo will charge to 4.2V. I only use the LiPo, even for my 3.6V.

I'd post the link to the battery university explanation of this but on the cpf app.


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## thedoc007 (Jul 10, 2015)

Mr Floppy said:


> The difference is 3.6V is lithium cobalt, the 3.7V is lithium manganese. On the above mentioned turnigy hobby charger, there will be a LiCo setting and a LiPo setting. Respectively 3.6V and 3.7V. The difference there is the LiCo setting will charge to 4.1V and the LiPo will charge to 4.2V. I only use the LiPo, even for my 3.6V.



Most of this is not correct. I can't speak to the specific charger, but everything else is general.

First, lithium polymer (LiPo) is a method of construction, which can be used with multiple cell chemistries. A LiPo could be LiCo, or lithium iron phosphate (LiFePO4), or something else. You CANNOT assume that a LiPo has a certain voltage without knowing the chemistry of the cell.

There is NO difference between 3.6 and 3.7 volt cells. It is simply a NOMINAL voltage, because every cell needs a reference point. In fact, either 3.6 or 3.7 volt cells have a fairly wide range. Fully charged, they are at 4.2 volts, and they can usually be discharged down to 2.75 or even 2.5 volts.

Lithium manganese (LiMn) and lithium cobalt (LiCo) both have a 3.6 or 3.7 volt nominal rating. You cannot tell which chemistry it is by that number alone. Some manufacturers have different nominal voltage ratings FOR THE SAME CELL. Why they do this, I don't know. 3.7 volt nominal allows a higher watt-hour rating, so most companies seem to use this, but there is no actual difference either way.

3.6*3400mAh = 12.2 watt-hours
3.7*3400mAh = 12.6 watt-hours

My Xtar VP2 has three settings:

3.2 volts (for LiFePO4) which actually charges to 3.6 volts max.
3.6 volts (for LiCo, LiMn) which actually charges to 4.2 volts max.
3.8 volts (for higher voltage cells, the LG D1 and E1 are examples, but there are others) which actually charges to 4.35 volts max.

You have to simply realize the rated voltage is a point within a broad range - you need to know the chemistry of a cell to determine which charge setting is appropriate. But the 3.6/3.7 volt debate is a red herring...there is no real difference.


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## TEEJ (Jul 10, 2015)

That 3.6 or 3.7 is just the AVERAGE voltage....or at least that's how it started. 


IE: They all start at 4.2 v, fully charged, and, discharge down to some lower voltage, and, the average is in between the upper and lower limits for the cell.

If a cell can discharge down to a LOWER voltage, it can lower the AVERAGE voltage proportionally.

So if two cells start at an upper limit of 4.2 v, and one can drop to 3.0 v, its resulting average might be 3.6 v.

If the other cell discharges down to 3.2 v, IT'S resulting average might be 3.7 v.

As most of the new cells, ironically, are able to discharge much lower, and, that in fact is often where those spiffy new high mAh come from...they use the 3.6 or 3.7 v as a NOMINAL voltage, so people don't get confused and think they are "lower voltage" cells...and, the PERCEPTION then becomes that a 3.7 v cell is better, because 3.7 is more than 3.6 v, etc.

When multiplied by the mAh...the perceived benefit is that you get a higher watt-hour result using the higher voltage, but, in fact, you can ignore the 3.6 vs 3.7 v label, as mere marketing.


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## Mr Floppy (Jul 10, 2015)

thedoc007 said:


> Most of this is not correct. I can't speak to the specific charger, but everything else is general.



Sorry wasn't clear enough, I am addressing the specific charger. The charger is 3.6V / 4.1V max for the LiCo setting. 3.7V /4.2V for the LiPo setting. There is also a LiFePO4 setting that is 3.2/3.6.

It mentions LiMn in the pamphlet they call an instruction booklet although the version of firmware I have only has LiPo. Written at a time I think when LiCo was still charged to 4.1V 

And as I said before, battery university has a good explanation of the 3.7V 3.6V difference. Although teej has done a pretty good job


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## WalkIntoTheLight (Jul 10, 2015)

TEEJ said:


> As most of the new cells, ironically, are able to discharge much lower, and, that in fact is often where those spiffy new high mAh come from...



I didn't know that. So, for most people that charge their batteries up when they hit 3.0v or 3.2v, they're not getting an extra benefit by buying 3400mAh cells?


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## thedoc007 (Jul 10, 2015)

WalkIntoTheLight said:


> I didn't know that. So, for most people that charge their batteries up when they hit 3.0v or 3.2v, they're not getting an extra benefit by buying 3400mAh cells?



That is not the case. For one, a cell is almost completely dead at three volts...you might be able to eke out another percentage point or two, but it isn't going to make a huge difference to usable capacity. Higher capacity cells also deliver more mAh from say, 4.2-3.6 volts, even if you don't fully drain it. (It is true that you won't get the FULL benefit of the higher capacity, but you will still see SOME benefit in most cases.)

Now, if you use your cells in high-drain applications, especially if you top them off frequently, you may actually get more usable capacity per charge on a (lower capacity) high-drain cell. This is because high drain cells typically have less voltage sag under load. 

The new Sanyo/Panasonic NCR18650GA and LG MH1 pretty much render this argument moot, for most purposes. They are each 3500 mAh, hold voltage well, and can deliver virtually their full capacity even under a ten amp load. They combine the best features of both types of cell.


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