Dual 18650 series/parallel battery marriage question

[Silver5656]

So do the dual 18650 box mods need to have married batteries? Is that true for both series and parallel builds? Is that only if charging together? I've read different things and just wanted to make sure it's correct.

For example. I have the sigelei 100w which is in series, BUT there is no charging built in. So I have to take them out to charge them. I dont see how having a married pair makes a difference?

I understand the basic concept. But since I am not charging through the device, and never it let it go too low, I dont see the benefit? Please explain

 

[Nomoreash]

Batteries wear over time and with the number of cycles they've been through, how hard they've been pushed, etc. A battery that has many charging cycles through it isn't going to keep a charge as long as a new one.

So yes you want to keep both batteries the same so they wear as evenly as possible. Start with a new set and always keep them together when in use and charging so they both have the same number of cycles on them, no matter if it's onboard or you remove them to charge.

 

[sando7]

i also alternate battery placement in the sled every-other time and in the charging slots on the charger.......i use a separate i4 charger just for my Sig batts and use the same 2 slots alternating every-other charge....and check the voltage coming off the charger keeping both the same and also labeled the batts "a" & "b" ect ..........been doing this with 4 new VTC5's. i bought about a month or so ago.

 

[Silver5656]

Batteries wear over time and with the number of cycles they've been through, how hard they've been pushed, etc. A battery that has many charging cycles through it isn't going to keep a charge as long as a new one.

So yes you want to keep both batteries the same so they wear as evenly as possible. Start with a new set and always keep them together when in use and charging so they both have the same number of cycles on them, no matter if it's onboard or you remove them to charge.

I understand this. But I dont see the "dangers" involved with this unless you run down the battery too low, or you charge, and even then its only in series, no? not parallel?

 

[Silver5656]

I understand the importance of the marriage. When I did rc cars, i knew the value of having matched cells. And the "big boys" used to run tests on individual cells, to make sure they were as closely matched as possible. I know that even buying 100 batteries of the same make/model in 1 box, does not mean that the cells are going to be matched. But when it came to RC cars, much more precision was required to gain that extra second of run time, or extra .01v. But because the sigelei 100w cannot be charged in series, and I never run it too low, I do not see the point of marrying batteries. And the same goes for the vaporflask, which is in parallel. My understanding is that as long as the batts are close enough (ie same age/make/model) that the batts will level off in voltage and draw down in parallel.

 

[edyle]

So do the dual 18650 box mods need to have married batteries? Is that true for both series and parallel builds? Is that only if charging together? I've read different things and just wanted to make sure it's correct.

For example. I have the sigelei 100w which is in series, BUT there is no charging built in. So I have to take them out to charge them. I dont see how having a married pair makes a difference?

I understand the basic concept. But since I am not charging through the device, and never it let it go too low, I dont see the benefit? Please explain

"Is that true for both series and parallel"

Parallel is supposed to be less unsafe than series batteries.


In parallel, the strong battery ends up topping up the weaker battery.

 

[Silver5656]

Hi edyle. I think you meant to say that parallel is more dangerous?

The way I thought, was that once the stronger battery tops off the weaker battery, then they are even. And in series, the weaker battery will always limit/hinder the stronger ones.

 

[edyle]

Hi edyle. I think you meant to say that parallel is more dangerous?

The way I thought, was that once the stronger battery tops off the weaker battery, then they are even. And in series, the weaker battery will always limit/hinder the stronger ones.

No.
I'm not the battery expert, but stacking (series) LITHIUM batteries has always been a no-no from what I've read here on ECF.
But putting them in parallel seems to be less of a concern; maybe you lose some money but you don't lose your face.



But yeah I see what you're saying:

And in series, the weaker battery will always limit/hinder the stronger ones

The big thing would be that once LITHIUM batteries drop below a certain value in voltage, things get dangerous and it's dangerous to attempt to charge them.

That's why regulated mods cut off at 3.3 volts; and most chargers won't charge your batteries if they're lower than something like 2.5 to 3 volts.

 

[Silver5656]

yea stacking is more dangerous, but i mean the ipv3 and the sig 100 stack the batteries.

And because most regulated mods DO cut off at about 3.x ish volts, I don't see the harm really. Yes, a mech with dual batts running low voltages I know is bad. But in a regulated? I dont see the harm. The only harm I see, is that instead of 200 charge cycles, it might decrease to like 180ish (or a somewhat similar percentage)

 

[edyle]

yea stacking is more dangerous, but i mean the ipv3 and the sig 100 stack the batteries.

And because most regulated mods DO cut off at about 3.x ish volts, I don't see the harm really. Yes, a mech with dual batts running low voltages I know is bad. But in a regulated? I dont see the harm. The only harm I see, is that instead of 200 charge cycles, it might decrease to like 180ish (or a somewhat similar percentage)

Series batteries (stacking) means the positive of 1 battery connects to the negative of the other battery; for a total of 8 volts.

Parallel batteries means you connect the two positives together and the two negatives together; same 4 volts as with 1 battery but you get twice the capacity.


You mentioned that the sigelei 100w uses two batteries in series but, I'm not so sure of that.

 

[Silver5656]

I do know the difference between series/parallel but it is good to mention it (always good to give information when its possible)

I am positive the sigelei and the ipv3 are in series. They buck down the voltage.

I did find some more evidence. Apparently, the harm of NOT matching cells comes when it is being charged. When being discharged (aka using it to vape) there seems to be little harm to the batteries (unless of course one battery is degraded significantly over the other).

Does anybody know if any of the on board charge chips that use dual batts balance charge? I'm going to bet no. In which case it is dangerous to charge ANY dual regulated mod.

A Guide to Understanding LiPo Batteries - Roger's Hobby Center - Radio Control (R/C or RC) Cars, Boats, Airplanes, Puzzles, Plastic Models, & Trains - Saginaw, MI

if you scroll about 1/2 way down it explains parallel vs series charging.

After reading this, I am hesitant to charge any dual regulated mod via the usb, and will be taking them out to charge.

Again, I want to ask, does anybody have any actual proof of safety?

 

[Silver5656]

Oh, and yes it is safer to have a married/matched pair of batteries when charging in series/parallel, but from my experience in RC, matched cells can degrade at different rates rather quickly, and thus using a built in charger w/o balancing will cause harm to the battery.

 

[Silver5656]

Lithium-Ion Battery Cell Balancing

This is a great video on NOT balancing cells. And because to my knowledge, NO dual mod balances cells, charging batts in series (even if they are matched/married) is NOT safe.

 

[sando7]

i just took my batteries out of my Sig 100 at 50% discharge according to the screen reading and checked them both with my DMM.
the one on the left side read 3.73 and the one on the right read 3.72...Sony VTC5's

 

[Silver5656]

but the sig has no charger built in. you are charging them individually, essentially you are manually balancing the batteries

 

[sando7]

that's exactly what i want to do, if i had on-board charging i would NOT use it........i just take my batts out at 50% and swap for fresh.
now i have been keeping a close eye on the charging voltage when pulling them off the charger making sure they both match voltage.
and what i have noticed so far is the right side of the sled seems to pull a small tad more voltage....but it's a minute difference.....i feel safe using my regiment.