18650 for a New Person

Note: I don't actually have any lights that use 18650s yet. I want to see if they're even worth the trouble.

1. There are 65/66 mm protected cells, 68 mm protected cells, and various unprotected cells. I was originally looking only for 65/66 mm cells because I was worried about having things fit in flashlights, but I notice the popular AW cells are 68 mm. I would want versatile batteries; in actual practice, how likely am I to run into a situation where my batteries don't fit with 68 mm cells? 66 mm? 65 mm? Is there actually a difference between 65 and 66 in practice?
2. Suppose I'm willing to risk it with some cheap batteries instead of AWs. There are lots of options online. What are the most current suggestions and warnings for that?
3. Are the main problems with cheap chargers largely mitigated by using protected cells and not leaving them on for too long?

I can only speak to your 3rd question.

Yes, and not only for "cheap" chargers. Any charger can fail (consider all the laptops and cell phones that have been recalled). Protection circuits can fail too, but the chance that both the charger and the cell would fail at the same time is twice as unlikely.

It is always a good idea to monitor Li-ion charging. I make it a point to only charge my cells when I'm home and awake. It's probably not necessary, but considering how little trouble it is, I consider it cheap insurance.

I would start by looking for a good charger such as a hobby charger. A good charger can analyze and tell you whether your cells are good or bad. Even the best and most expensive cells will not be able to tell you how your charger performs - except perhaps by going poof if have a bad charger. :devil:

- panasonic-sanyo makes the best li-ion rechargeable batteries but they come unprotected
- cheap chargers are okay as long as u make sure they don't overcharge
- short circuiting will cause fire / explosion for SURE
- u may probably need to buy an inexpensive digital multimeter as well

Bat said:

- u may probably need to buy an inexpensive digital multimeter as well

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Ah, yes, thank you for reminding me:

I may be new to good flashlights and esoteric batteries, but playing with a multimeter is totally fine. That's another reason I'm willing to use cheap chargers.

DreadArchon said:

There are 65/66 mm protected cells, 68 mm protected cells, and various unprotected cells. I was originally looking only for 65/66 mm cells because I was worried about having things fit in flashlights, but I notice the popular AW cells are 68 mm. I would want versatile batteries; in actual practice, how likely am I to run into a situation where my batteries don't fit with 68 mm cells? 66 mm? 65 mm? Is there actually a difference between 65 and 66 in practice?

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Unprotected cells are 65 mm, protected are 67 to 70 mm, you can see the size of many cells here in my 18650 roundup. All protected cells are based on 65 mm long cells where a protection circuit is added and sometimes there is also added a button top.

DreadArchon said:

Suppose I'm willing to risk it with some cheap batteries instead of AWs. There are lots of options online. What are the most current suggestions and warnings for that?

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Many people are using the flame colored Trustfire.

DreadArchon said:

Are the main problems with cheap chargers largely mitigated by using protected cells and not leaving them on for too long?

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Depends on what you define as the main problem.
Many cheap chargers charge the cells to much, i.e. they charge them to 4.2 volt, reducing the lifetime of the battery.
Some cheap cheap chargers does not have a very safe construction, i.e. they can not be UL or CE approved and might have fake CE/UL marking.

The general safety rules are:
Do not charge unattended.
With a new chargers, use a DMM to check the charged voltage, it must be below 4.25 volt.
Use a DMM to check the battery voltage before charging, if the voltage is between 0.2 and 2 volt the battery is damaged and might be unsafe (A 0 volt reading probably means the protection is tripped, it just has to be reactivated).

HKJ said:

All protected cells are based on 65 mm long cells where a protection circuit is added and sometimes there is also added a button top.

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Does this mean that flashlights are built to be able to take 68 mm batteries with button tops, then?

I'm actually even more worried about buying batteries that won't go in the flashlight than I am about batteries that die or explode. I don't know how important it is to get button top or flat top or shorter than 68 mm or... etc.

DreadArchon said:

Does this mean that flashlights are built to be able to take 68 cm batteries with button tops, then?

I'm actually even more worried about buying batteries that won't go in the flashlight than I am about batteries that die or explode. I don't know how important it is to get button top or flat top or shorter than 68 cm or... etc.

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I have never seen a light for a 68 cm cell .

Lights for 18650 are usual designed for the 65-68 mm range, some for longer cells. All lights will work with button top (But they are usual the longest cells) and many does also work with flat top.
The AW18650-22 does work in just about everything.

DreadArchon said:

Does this mean that flashlights are built to be able to take 68 cm batteries with button tops, then?

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Generally you will be OK with 67-68mm cells, but 70mm cells may be too long for some lights. All lights I've ever seen use a spring to hold the cell - that spring can be compressed a little more for a longer cell. Flashlight manufacturers are aware that there is some variation in the length and width of batteries and make their lights to accommodate a normal range of cells. If you go to the fattest & longest battery you can find (in the 18650 size) then obviously you could have a problem with some lights.

According to HKJ's chart the AW 2600mAh cells are 67.5mm - they fit fine in the Zebralight H60w, Olight M20, Ultrafire WF-501B, MG PLI and Jetbeam Jet-IIIM. Those are the only lights I've tried and the cells fit each of them just fine, the Jet-IIIM needs a button top though.

I have some Trustfire black/red cells which HKJ lists as 68mm and they are tight in a cellphone charger (charges a cellphone from an 18650) I have, only just fitting without even 1mm to spare - I wouldn't be able to get a 69 or 70mm cell into that device. I would suggest sticking to the 68mm & below sized 18650 cells if possible.

HKJ said:

I have never seen a light for a 68 cm cell .

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That was a funnier typo before I looked to my left and saw something from the bottom of this chart on my floor. But, yeah, fixed.

And: Thanks everyone, my questions are answered!

Being familiar with a DMM shouldn't be viewed as a "get out of jail free" card allowing one to use a poor charger. You need to ask yourself if you'll ever leave your charger unattended. Fall asleep with cells on the charger. Go away for a weekend with cells on the charger (oops, I forgot).

Better to get a decent charger known to terminate and not overcharge, ideally one that actually uses the recognized charging algorithm. Consider an investment in a decent charger as "oops protection".

HJK has an excellent overview on how to use your DMM to investigate things. Worth a read regardless of knowledge level.