Quality protection. Like Evva or keeppower which use seiko protection chips.
With series cells it is easier for things to go very bad. If the cells aren’t matched then one can reverse charge the other. Matched requires the cells to be the same band, model, capacity, voltage, internal resistance, age / wear. Always used together, charge together and stored together. Even then you need to monitor them to ensure they remain matched. Quality protection should save you if something goes wrong. Some people do series unprotected, it’s ok for them to take on the risk themselves, perhaps they are OCD about keeping them matched and regularly check internal resistance, but personally I wouldn’t advise random people to do series unprotected. You don’t know how careful others will be.
I'm more afraid of protected cells than unprotected, mainly because of the razor-sharp strap that runs from the positive pole, over the crimp at the top, and all the way down the side to the PCB at the tail. All the protected cells I have disassembled have had nothing between that strap and the case but a piece of Kapton tape.
For me, Panasonic/Sanyo NCR (same batch and matched) “Unprotected” is the best
Murphy’s Law (according to g_sintornillos): If you use “Protected” batteries you are unprotected. You will stay in the dark at the worst time in the worst place.
Have there actually been any recorded incidents caused by the strip from the positive to negative ends of protected cells?
The strip along the side is attached at the top and bottom. Since it can’t move there won’t be any wear to the kapton layer under it. Never seen a report of a short through that kapton layer. It’s not at all concern imho.
I’ve seen people report protection that fails in different ways but from what I’ve seen it’s always the cheap junk protection chips. Batteries with clear shrinkwrap over the original cell wrapper and unknown protection added by mystery companies. Big surprise if they fail. Instead get seiko protection by Evva or keeppower (the two who have the lowest prices for quality cells + seiko chips).
And if you’re in a real emergency situation where your cheap protection fails, try just ripping off the protection. Hopefully you have a knife. If not try using your keys carefully.
And we are talking about series cells here. You might worry about some potential issue with protected cells. But it’s not a reason to tell people to go series unprotected imo.
Protected cells are for series use. All the issues really have been #$^&fire cells. Matched quality cells have never generated an issue that I’m aware of. I still personally use protected cell for most lights, especially the ones I make for others. PCB also keeps the cell from over discharging. Multi cell series light I like PCB’s even more. If it’s a light I’m experimenting with than I’m probably not using PCB’s but I am constantly reading current and voltage. I’m comfortable with my skill level. My batteries are also only Panasonic or Sanyo in 18650’s. I’ve got a modded Trustfire TR-J20 at first the three 26650 cells stayed close together but after about 15-20 charges I’ve got a cell that’s a lower voltage than the other two. Those are 5200 Keeppower and they are PCB’ed.
Who would think it’s a good idea to just toss a loose li-ion in your pocket with anything metal?!
If you are treating your li-ion properly, imo there should be little to no wear on the wrappers. New flashlights should be inspected for burs / rough edges. Batteries should never be forced into a light, some high capacity cells are slightly thicker. Loose li-ions should never be stored with any random metal objects. If you want to carry an extra cell in your pocket, get a case. You can even make a protective sleeve with shrink wrap. Cut a piece ~45mm long, slide over 18650 so one end is at the middle of the cell, shrink the other end and fold over neatly while still warm. Repeat to make a 2nd one. You now have two sleeves, each one completely covers one negative or positive end and they meet in the middle.
Follow the links, we find e-cig users and pictures of unprotected purple efest 18650s.
As for li-ions in the mail, well they have been banning li-ions shipments because chinese sellers package them so badly. People have posted pictures on BLF of multiple cells just loose in a thin envelope and the metal cells coveted in dents! Protected or unprotected, li-ions must still be treated properly.
Again we are talking about series cells here.
For single cell lights, unprotected can be fine as long as you’re a careful person, all your lights include low voltage protection and you only use quality chargers. Like ones tested by HKJ.
I use protected batteries in flashlights that have multiple cells in series.
When you buy good quality cells there isn’t much difference in price between protected and unprotected cells; especially when you divide that number by the 500 or so charge/discharge cycles.
If you are wondering about a specific flashlight you can always contact one of the brand reps here or on CPF and they will be happy to recommend what should be used in their flashlights.
Bob
