I don’t believe this is unique to the P42A. I’ve seen the same thing on Samsung and LG cells.
When removing nickel from reclaimed packs I’ve accidently sparked the area marked in red as the plastic insulator doesn’t go all the way to the edge.
I don’t know if it really matters for pack building. Probably worth putting a fish paper ring on for added protection though
The ring on the 30q is definitely not the same as this one that @ducktaperules is talking about
But yeah it doesn’t really hurt
Aren’t they both just plastic rings?
Maybe - the ones on the 30q are very thin though.
I have to imagine if @ducktaperules is specifically mentioning only the P42a, specifically the black ring, that they are at least thicker on the P42a
So my understanding is that these plastic rings are better for abrasion resistance but not as good as fish-paper at dealing with heat.
My personal thoughts is that if your nickel is reaching temperatures that are hot enough to melt that plastic insulator then really you’ve already got bigger issues.
And i personally don’t think the 30q, or most other Samsung cells, need fish paper rings in a well designed pack. In a well designed pack there should be little to no opportunity for any fault to occur where the internal plastic ring would not be sufficient.
That said, i would still recommend FP rings to novice pack builders as it cant do any harm to have extra protection.
I’ve tested these rings with abrasives and sharps, and they aren’t as robust as FP. They slice pretty easily, and don’t gum up an abrasive like FP does.
With regard to heat, it’s sometimes a factor when packs have soldering near the edge of a cell. Compression from certain nickel installations may end up squishing the plastics as they deform under heat.
That’s not to say your specific pack encounters this, it doesn’t look like it does.
However that’s not an uncommon scenario for commercial packs, and I’ve become more familiar with them this year.
So I don’t think it’s necessarily to say that Molicels don’t require additional insulation. They seem to be more robust than other cells, absolutely, in that area.
However the requirement of an insulation ring remains more so a factor of the pack design and assembly than the quality of plastic a cell manufacturer uses.
How are all of you guys leaving your batteries to die 
omg does everyone not constantly check all of their batteries like twice a day? Just me?
Twice a day?? Someone has control issues here lol
I do it maybe once a week if I don’t ride the board.
Paranoia Lol is more like it
Agreed but again you shouldn’t have sharps floating around near the ends of the battery in a well designed pack.
Yeah there is huge variance in “commercial packs”. I have seen some packs that are amazingly designed and others that you can tell were built in china by the lowest bidder. I have seen “commercial” ebike packs that most novice battery builders here wouldn’t even considering storing in their house.
This is the key really and im in full agreement, the pack design makes all the difference. If the designer has considered these things then additional protectors serve no purpose. If the pack is being built in a way where these parts of the cell can be exposed then it cant hurt to add them.
This 
Especially if you are making a flex pack, you need these rings to protect from the heat of soldering the series connections…
I assumed the rings were for if you accidentally miss your weld on the positive end, so you dont weld the + to the - , among other uses
I gunked up my original reply, so I’ll just redo it. My apologies…as if anyone actually cares.
Well sure, but ifs abound, and writing the addition of insulating rings on manufacturing instructions costs essentially nothing to the client.
Agreed, but things happen. It’s a similar vein of precaution as a seatbelt or airbag.
I can’t account for what a battery customer does with an eskate pack or what it’s subjected to, or how it’s installed or what’s around it.
And I do agree with your stipulations. However a battery builder may want to account for things outside of their design. Accidents, harsher use, etc.
While I understand we’re all just speculating here, and toying with ideals, it doesn’t seem particularly costly to add them. And at least for the variety of things I’ve encountered, realistically, it’s of little use to hinge on the assumption that the P42A’s plastic rings are going to cure what ails the risk bubble of a battery.
We are never going to agree on a single set of battery-building rules for every case scenario. This is a complex science with a bunch of unique situations. The pack that started this conversation, I think, is fine. I’d happily keep it in my home and sleep soundly.
Wonder @Battery_Mooch opinion on insulator rings?
Sure, that pack is excellent.
I’m suggesting that to say “Fish Paper rings are not needed on the Molicel P42A cell” is not an entirely correct thing.
the insulator rings are literally designed and intended to isolate the negative edge of the top of the can from the positive assembly in the middle. unter the insulator ring is just ~1mm of separation, so that insulator ring provides more separation between negative and positive. it’s meant to be non-conductive and that’s it.
always use them though, a cell without an insulator ring is essentailly dangerous.
Take a look inside high end commercially made battery packs. Bosch bike batteries, high end power tool packs. Makita, Milwaukee etc.
Definitely a case for using rings in a lot of cases, but in solid, well designed packs they don’t seem to be used.
Power tool batteries aren’t usually subjected to the same kinds of lives as many eskate batteries, may not be the most appropriate analog.
For my own curiosity, what classifies a high end pack? Or a well designed one? Is one that’s designed with the step of adding insulation rings considered not well designed?
The engineer I’ve been working with had drawn cell frames specifically measured for the cell with the insulator ring, as he wanted them there. These are relatively serious packs for things much more…critical than eskates or drills.
While it’s only a single case in terms of design/company, it’s a decent enough example that want of insulator rings isn’t necessarily tied to good or bad design, or level of work.
As time goes on and I churn out more and more batteries, the only answer to these kinds of questions that I’m personally comfortable giving is some form of “it depends”.
In a forum where folks are at different levels of DIY building, it doesn’t seem like good all-around advice to say that any particular cell is fine to just weld up and wire together without insulator rings, especially when it’s a minor step and such a small expense.
And while I certainly no interest in drawing any more ire due to this topic, I don’t think what I’m saying here is unreasonable or ill-informed.
Quite honestly, I think this sinks any argument you’ve made brother.
I get it, a properly built, well designed pack likely doesn’t need the extra protection. But this isn’t the case of two condoms is worse than one. When you can add a little extra something to make your builds just a bit safer why wouldn’t you?
By my own estimations you’ve likely spent more time today typing a discussion on the topic than you would applying rings to a pack. Not to mention they cost pennies a piece, so it’s most certainly not breaking anyones bank…
You, and Apex I guess, are the only builder in this community of that opinion that I’m aware of, it seems like a rather odd hill to go to war over.