Hello
About battery: could we have an exact model recommandation ? The one that would be the best capacity, perfect fit, safe, easily ordered on any website…
Thanks you
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This is not as easy to answer as simply saying this is the best brand and model, Unfortunately. 18650 batteries come in a variety of chemistries and some offer protection circuits while others do not. I think this is important enough to not just state, but to do so while making extra effort to make a point. I will highly recommend you study up some. Everyone here will recommend that if you are new, opt for protected cells. These cells sacrifice a tiny bit of capacity to store a chip that prevents overcharge/discharge and heat protection which prevents the cell from possibly shorting out or worse, exploding. Avoid at at costs bootleg cells (especially anything with FIRE In the name…)
There is a ton of info with testing results here:
-------------- Mooch’s battery blog
-------------- Mooch's blog | E-Cigarette Forum
Here are some more resources:
EVERYTHING YOU NEED TO KNOW
protections
chemistry comparisons
battery guide (i actually get my batts from here)
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After you’ve read some of that… if you have any specific questions… I’ll do my best to answer them
all that aside… if you want a charger recommendation…
I can easily and wholly recommend the XTAR PB2S 2 bay charger. It will charge one or 2 cells at a time, you can use it as a backup powerbank charger to charge your phone, it charges REALLY fast (the fastest one i have currently) AND (should you decide to venture this route) it supports charging both protected and unprotected cells (i wouldnt mix and match though… thats usually a bad idea in general)
Even mixing same brand, same type but different usages is a bad idea.
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i should have clarified that Mix-N-Match in regards to batteries… in the most generalized sense… brands, models, chemistries, ratings, voltages, capacities and even ages… NEVER mix anything that doesnt match
The short and simple is that when you figure out what you’ve settled on, get new and in pairs (because that is how you will use them in the DT… in sets of 2 {I purchased 8})
I have even went so far as to rewrap these four pairs with labels to further differentiate them, but i digress… rewrapping batts is a post for another occasion.
I will add that there are only two notable brands that sell trustworthy cells that offer pcb protection
Nitecore
&
XTAR
and only the button tops offer this feature
as an example…
(THIS IS NOT A RECOMMENDATION! please do your own research)
Here are the differences between these two:
Nitecore NL1832 18650 3200mAh Battery - Protected Button Top
|Nominal Capacity: | 3200mAh|
|Discharge Current: | 6A Max Continuous (PCB limitation)|
|Nominal Voltage: | 3.7V|
|Maximum Voltage: | 4.2V|
|Approximate Dimensions: | 18.6mm x 68.9mm|***********
|Approximate Weight: | 50g|
Nitecore NL1834 18650 3400mAh Battery - Protected Button Top
|Nominal Capacity: | 3400mAh|
|Discharge Current: | 6A Max Continuous (PCB limitation)|
|Nominal Voltage: | 3.7V|
|Maximum Voltage: | 4.2V|
|Approximate Dimensions: | 18.4mm x 69.1mm|*********
|Approximate Weight: | 47.4g|
Upon close examination, one would notice that by gaining +200mah, you also gain some height and risk not being able to fit these in the battery holder.
which is why im trying to so hard to go the extra mile to encourage you and others to study up on this subject.
CWPi states this about their battery module. It does mention 2 types of protection features as well as dimensions for size batts it can hold… This is important and pertinent information to not take lightly when looking for these types of cells as they may vary among manufacturers.
"We carefully designed the battery holder to make it more compatible with various 18650 battery sizes: Φ18±0.5mm diameter, 65-69mm length. The battery module has “Short Circuit and Reverse Polarity Protection” features, but you are still advised to purchase* the batteries from a reliable distributor and install them correctly.
Theoretically, you could use a single 18650 battery to power the system or replace the batteries one by one even when the system is in use. These actions can still cause system instability, and we strongly recommend replacing the batteries after the system is powered down. Please remove the battery if you do not use the device for a long time. Please consult the battery supplier for detailed 18650 safe usage rules, and please strictly follow them"
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Thanks for all these informations.
One last question: can’t Clockworkpi gives an official recommendation? 
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I am sure they would have done so… however, they likely refrain from doing so for the reasons I’ve stated.
Anyone else wanna step in? samewise consensus? recommendations?
I will state that I have personally chosen unprotected cells… but I am seasoned with matters of electrical engineering.
If you want to discuss various protections, chemistries and other differences… or have queries about any of these… im ready
Apologies - The browser I use rolled up your response… So I didn’t see all the detail… appreciate the time it took to answer these questions to the extent you did.
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batteries? check.
charger? check.
storage? did we go over that yet?
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Will these work?
I drilled a hole in some pill bottles and glued them in to end… now I have safe storage for several batteries… in my quest for batteries (before I read your battery summary) I ended up with several LED flashlights that came batteries - now I’ve got them stored so they don’t short out and catch fire…
If people are hesitant to recommend models, I can least attest to batteries that don’t fit…I had picked out Nitecore NL1834 3400mAh dia 18.7mm. Seems a few mm to wide to have the battery cover fit. Just to discourage anyone considering this model from the advice above…
According to their website even the 2300mAh Nightcore battery is also 18.7mm dia. So maybe stay away from current model Nightcore?
edit just want to clarify to keep information consistent on the forum. The NL1834 actually do fit. Just make sure the batteries are seated as deeply as possible
My research led me to buy Sanyo NCR18650GA with protection circuit and button top. Dimensions 18.5mm x 69.5mm. They just barely fit, and I can’t get them back out without a spudger. The battery compartment lid does stay closed, but I have to insert it awkwardly.
At a minimum, I think I’d skip the button top if I were doing it again, and probably find a smaller battery altogether.
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So to further clarify the NCR18650GA are unprotected cells? Earlier I assumed that the Devterm had it’s own on board BMS, for battery protection. And then I came across this information from one of the mods:
But according to the website:
“The battery module has “Short Circuit and Reverse Polarity Protection” features, but you are still advised to purchase* the batteries from a reliable distributor and install them correctly.”
obviously @redshift has yet to burst into flame. This is my first encounter with 18650 cells and I’m trying to do all my research. Signs indicate unprotected cells are probably cool? But I’d like to be safe, after such a long wait 
So far I haven’t found a protected 18650 cell that is less than 18.6 dia (nightcore, fenix, samsung) It would be cool if Clockworkpi can’t sell the batteries due to logistics (Honestly!! I fully understand) If they could be a bit more specific on their recommendations, what’s a suitable capacity Xmah, protected or unprotected cells? Flat or button top?
to be clear, the nightcore cells I got work, and my devterm powers fine. Just the battery cover doesn’t close. it does close
I think you can get them unprotected, but mine have the protection circuit. I would definitely not recommend getting unprotected cells. As @Godzil said, the DevTerm’s protection circuit protects the DevTerm, but you have to worry about batteries outside of the DevTerm too, for your own safety.
I’d really appreciate if more users would post what batteries they use that work (or not). It seems really difficult to choose a model that you can be sure fits inside the DevTerm, with the dimensions given on online sites (when they are given at all) sometimes contradicting themselves on the same page.
I would also prefer to get protected cells, but those seem to be even harder to come by and are generally larger, so more risky that they fit. Unprotected ones are much easier to find. So some more substantiated info on what the actual risk is using unprotected cells would be much appreciated.
I have used the following batteries with no issue: https://www.sparkfun.com/products/12895
I ordered these back in July, when they were in stock. I don’t believe Sparkfun ships internationally, but their distributor, Digi-Key, does, and has about 600 in stock: https://www.digikey.com/en/products/detail/sparkfun-electronics/PRT-12895/5271298
These batteries are specified to be 0.72" Dia x 2.56" H (18.2mm x 65.0mm), but measured to be about 18.37mm, as shown below. Fitted in the devterm, this seems to be the maximum size if you want to use the included injection molded battery cover.
This is the given datasheet with model numbers and specifications: https://cdn.sparkfun.com/datasheets/Prototyping/ICR18650%202600mAH%20datasheet.pdf
Again so these batteries do not have a protection circuit. The discussion on the product page indicates the purpose of these is to be assembled into battery packs. I’m curious to see how these work out for you in the long term. Unfortunately these particular cells are not available to Canada, via digikey.