And some would make the very legitimate choice to say, "Why take the chance".
Personally, I buy protected batteries and I have "stacked" them. Would I stack unprotected batteries? That remains unseen... I don't have any to stack.
However...
I have seen cars crash into each other and I still drive.
I have seen Airplanes crash on the news and I still fly.
I have heard of people getting parasites from uncooked food, yet I still enjoy Sashimi from time to time.
Does a gas pump explode occasionally? Sure it does... yet I still put gasoline in my car.
There are a great many dangerous things we do in our daily lives without so much as a second thought.
According to NOAA.. In the United States, an average of 58 people are killed each year by lightning. Hundreds are permanently injured. Imagine the statistics worldwide?
When there is a better chance of being struck by lightning Than having a battery explode due to "stacking"... What exactly are we worried about?
But with all this talk about unsafe behavior, which most of us do daily, I am not actually saying that using "stacked" Lithium Ion batteries is actually unsafe!
There are millions of devices in service today that we use in our daily lives that are powered by "stacked" batteries, some are called "unprotected" though they will have the following safeguards built into them:
shut-down separator (for overtemperature)
tear-away tab (for internal pressure)
vent (pressure relief)
thermal interrupt (overcurrent/overcharging)
If THESE safeguards fail, some cells also offer what we have been calling "protection circuits"... these are at the negative end of the cell increasing the length by 2-3mm...
There have been millions of faulty LiOn batteries recalled, the vast majority due to batteries that were found to be susceptible to internal contamination by metal particles. Under some circumstances, these particles could pierce the separator, causing a short-circuit. A short circuit remains the single biggest threat to a Lithium Ion Battery, because it can cause rapid thermal runaway, which NO protection circuit will stop in the right circumstances. Just as you are powerless to prevent being hit by lightning, shy of avoiding it entirely, the only safeguard against an internal short in one of these cells is to abstain from using them entirely.
I have seen absolutely no scientific evidence that points at "stacking" as the cause of LiOn battery failure. Batteries of all chemistry types have been used in series circuits (or stacking as referred to in eCig lore) since the battery was invented. Your car battery is a hybrid stacked design with 6 cells at roughly 2V each... all with a common chemistry bath.
As has been stated before in this and many other threads, Your laptop "battery" is a power pack of several of these cells in a combination series parallel circuit that would make quite a bomb if abused... but the key word here is "abused". A portable drill with these cells has much the same configuration. So called "stacked" Lithium Ion battery packs are every where, and they are becoming MORE prolific... not less.
If a person says they will NEVER use "stacked" Lithium Ion batteries they need to toss out their laptop immediately. Too dangerous...
OK, so... is it wise to err on the side of safety?
Absolutely... But in MY mind safety needs to be focused on preventing the single most common threat to a Lithium Ion cell... A designer of eCig Mods needs to address and avoid the risk of SHORT CIRCUIT, at all costs!
Here is what I would suggest with regard to using these devices in eCigs.
1) Don't buy a purely mechanical Mod... EVER: (and I mean it!) The risk for an unprotected short circuit is ever-present. and in the event of a short, it's going to be a problem if the interal protection of the cell fails. When used as designed, these devices SHOULD be safe... emphasis on SHOULD... If a cell fails due to a short in one of these. it will really take the edge off your day...
2) Buy a Mod with Safety Designed in it: A Mod with safety measures built in is your BEST line of defense against a battery event. A well designed safety circuit will monitor for current draw, shorts and reversed batteries. It wil ALSO have a timed cuttoff to prevent over heating. Don't buy a "wired" mod that lacks over-current protection and short-circuit protection. Simple switch and wire mods present the same threat as mechanicals, compounded by the threat of poor wire management. In the event of a short circuit the wire can heat rapidly, thus melting the insulation causing a more serious and undetachable short circuit.
3) Magnetic Spacers are a No No: Absolutely NEVER use magnetic spacers on the positve end of a cell in a metalic tube OR metalic box mod OR between Cells in a series configuration... This is an unprotected short just waiting to happen, and when it DOES happen, it MAY get really UGLY... IF the internal safetly measures present in ALL Lithium Ion batteries (protected or otherwise) happens to fail.
4) Properly Dispose of damaged Lithium Ion Batteries when they have been compromised: Batteries are pretty cheap when compared to cosmetic surgery... if you accidently short one, physically damage it or expose it to extreme heat... THROW IT AWAY... and DO dispose of it properly! I cannot stress this enough. Physical Damage to the cell is probably the biggest cause of internal short circuits and internal protection failure. THIS isn't worth the risk... ever.
5) Buy your Mods and PVs from REAL businesses. A real business will carry product liability insurance. If you are a DIY person that knows what you are doing, then you KNOW it's been built safely and built correctly and you assume your own risk! If you have no clue what you're doing when building a mod... ANY mod... ask somebody with a knowledge of electronics to inspect the device BEFORE putting a battery in it. You may have wired a dead short in there, and if you don't understand electronic circuitry, you will probably never see it... an expert can see it without too much fuss.
6) When all else fails... use common sense!
I have specifically NOT mentioned to avoid stacking as a general safety precaution because in many well established industries the pracice of using Lithium Ion batteries in series circuits is as common as the day is long.
And that's how I feel about it...
