@Retro you are most welcome, i like the approach he takes to his testing. he also seems to give well reasoned opinions which can be difficult to come across these days!
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This is great! I’m a subscriber to Product Farm but I must have missed this episode. Thanks for sharing!
Based purely on past experience I like the Panasonic NCR 18650B. That battery was not tested in the video but I was surprised that the Japanese Pana/Sanyo did as poorly as they did.
Edit
(Edit: I’m removing this comment because it can be taken out of context. I use battery cells in industrial/medical devices; consumer electronics can use cells with 30+ or 40+ Milli-ohms of resistance.)
I will say that when I probe a battery and it’s internal resistance is over 25 mOh I start to consider it “not fit for use”. So if I had a new battery in my shop and it’s life started at over 20 I would send right to the recycling bin.
6 of the batteries claimed to be “brand new” but are either built with poor materials and quality controls or are used batteries that some one is selling on the second hand market as if they are new. (Sometimes pealing off the old shrink rap and replacing it with a rapper claiming 9999mAh lol)
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yeah i’ve been subscribed to him for a while now! and i will keep the panasonic ncr in mind when i’m laying in battery stock for my devterm!
Jehugarcia is also a nice channel to learn about batteries, years ago I watched alot of his vids like
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That would mean that the whole system is powered with 3.6V
Would it be enough to drive the screen?
What’s the problem with that? The voltage of lithium battery is between 4.2 (shortly without load at full capacity) to about 3.4-3.5V with no load at low capacity. (A load can lower significantly the voltage across the battery)
Because the battery are 3.6-3.7V on average you think you cannot power thing that need a higher voltage?
Then how do you apply the 10-20 kV needed on a CRT screen from your main 110-240V?
There are plenty of way to make higher voltage either in DC or AC, and I’m pretty sure theare are LCD panel that can work at 3.3V or 1.8V.
Maybe you are talking about the backlight? Well even with the two cell in series (which is the most likely scenario) you have just 7.2V on average which may not be enough depends on how the LEDs for the backlight are connected. It is more than likely that there is a step up voltage regulator for the backlight, either on the main PCB or on the LCD panel itself.
So I’m not sure what is the problem?
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Or maybe because I doubled the capacity and “you can only do that if the cells are in parallel”? Well.
yes, and no.
I should have worked in Wh instead of mAh, but the total power two battery can deliver is a simple addition in Wh. You always double the capacity whatever the scheme, series or parallel, what change is the output voltage, but as we are not using it in at that voltage whatever the way the battery are connected, it is a bit useless to look at that directly.
It would be true it does not work if the whole system was to work at 7.2-ish volt. it is not.
And honestly the 500-600 that was reported after was on raspberryPi, so probably on the 5V that goes in, so at 7.2V, for the same power the current would be lower, so it’s about the same order of magnitude.
But ok, so our example raspberry pi consume 600mA at 5V, that mean 3W
3W at 3.6V is about 0.8333333 A
3W at 7.2V is about 0.4166666 A
Now a single cell is about 3Ah so 3A * 3.6V = 10.8Wh, we have two cells, so we are now at 21.6Wh.
21.6 Wh / 3W = 7.2h.
Let’s see
In parallel we have “6000 mAh” of capacity. 6 / 0.833333 ~= 7.2 ! Oh magic!
In series we have “3000 mAh” of capacity: 3 / 0.416666 ~= 7.2 ! Insane!
Weird isn’t it?
As for what voltage the screen to take? I invite you to look at the mainboard schematic (the one that take the core module) here:
It does not says what is the battery voltage sadly, but clearly who that all the main voltage are 5V, 3.3V and 1.8V, and you can even find the one for the display!
Fancy!
But yeah, I even made a mistake in the original post for some reason i can’t explain. To drain them you need 2000mA for 3.6V, if they are in parallel, to deplete them in 3h, and 1000mA at 7.2V if they are in series, but both represent the same power: 7.2W, and that is a lot.
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i wonder if i could somehow manage to run whatever os i could make the lightest, still do what i need, and still be underpowered enough to hot swap the batteries with no fear of glitching…
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Do we know how much current the DT draws? At idle and when loaded. Not sure if this was said anywhere. Could probably guess based on the sum of the component’s datasheets.
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I wonder what the possibility of getting more battery modules and stacking/wiring them to run in parallel…
Where would you like the extra cells to be? Obvious spot seems to be where the printer module is. Or maybe design an enclosure that snaps to the back that could fit like 10 cells.
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I was just thinking, like, right on top of the existing one. and yeah, print a back that can accommodate stacked modules like that.
shrugs
i gave it some thought… but not nearly as deep as all that.
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I have some ideas but are top secret 
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Just in case someone runs across this thread later, my A06 DevTerm has 5800mAh batteries in it, and the Ubuntu menubar battery widget estimates 8 hours of battery life.
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Running two 3500mAh cells and also getting the 8 hour estimate. Anything above 3600mAh is a made-up number.
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Yep, I bought some ‘9900’ mAh batteries early on… I think its off by a decimal place so they are like 9900 x 10e-1 mAh …safer bet is to buy from a reputable source rather than Amazon… next you’ll ask me who and I’ll have to research my thread. I need to go and recharge mine since I’ve had them so long anticipation of the unit arriving.
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The best way to know the exact capacity of a battery is to have a proper charger that give you how much energy it put inside the battery.
Will not recommend any specific brand, but they are reasonably easy to find.
The best are of course the one that directly support the 18650 batteries without an adapter 
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Do we know how much current the DT draws?
My A04 draws anything from 3W to 11W depending on settings and workload. Printing also takes a lot of power obviously.