[HTC 10 Accessories] lagittaja:
Choetech has stated they're using Samsung Li-Ion cells so they're likely these. I'll crack open mine when I receive it, haven't ordered it yet.

http://gamma.spb.ru/media/pdf/liion-lipolymer-lifepo4-akkumulyatory/ICR18650-26H.pdf

http://lygte-info.dk/review/batteries2012/Samsung ICR18650-26H 2600mAh (Pink) UK.html

-26H is the successor to -26F

http://data.oomipood.ee/kasutusjuhend//ICR18650-26FM.pdf

http://dampfakkus.de/akkutest.php?id=120

http://lygte-info.dk/review/batteries2012/Samsung ICR18650-26F 2600mAh (Pink) UK.html

I personally have these -26H's inside my 4x18650 5V2A power bank case.

They're great cells for indoor use and low current draw (per cell) use.

They'll happily dump over 90% of the specified Whours even at a full 5A discharge. (which is 2600*3.63/1000=9.44Wh)

At a more sane discharge current of 1A/2A they'll be able to provide ~ 99/96% of the specified Whours.

So how much is really inside? Spec sheet says 10200mAh's assuming 0.2C discharge and 2.75V cut-off.

In practice? ~10200-10600mAh's depending on the discharge current. (this is of course fresh cells, capacity will drop over time)

This of course does not take into account the power loss which occurs when you boost the voltage up.

Assuming a nice, above average 90% efficiency inside the power bank you'd be looking at ~9200mAh's.

Then taking into account the voltage stepdown happening inside the phone, let's assume 90% efficiency again and we'd be looking at ~8150mAh's.

Aaand then taking into account the cable loss (- connector losses), let's assume you have an average 26AWG 1 meter cable and you transfer 18W of power at 9V2A, loss is 6%.

We're down to ~7550mAh's.

Saying it can charge a 3000mAh battery twice plays nice with that calculation.

One thing to note though and like I said, great for indoor use but if you look at the spec sheet, you can see the capacity vs temperature table.

tl;dr if you wish to extract every little ounce of power you can from these cells (or this power bank)

if you go hiking in really cold weather, make sure it stays close to room temp (25C), so not in the outermost compartment of your backpack but neither touching your body which could then warm it up higher than room temp - no es bueno.

if it's a really warm, sunny summer day and you go have a beer outside sitting in the porch, don't leave the power bank in direct sunlight, place it in shade instead

This is pretty much business as usual and has to do with the design of the cell and cathode material used.

Cells [like the -26H] intended for laptops, power banks etc. are going to have different discharge characteristics compared to cells [like INR18650-25R] intended for electric vehicles, power tools and so on.

So it's good that the power bank has an aluminium chassis. It's going to be able to dump some of that heat generated by the boost circuitry in to the air and so on and so forth.

The cells themselves won't really heat up that much. You know, there's 4 of them in there and they are in parallel = current load is being split pretty much equally.

At 3V under load which is pretty close to fully discharged (cut-off = ~2.75V), if the power bank circuitry is prodiving 18 watts of power and drawing 21.6 watts (18+20%) from the 1S4P battery pack because of inefficiencies, it would still be just 7.2A of current total and 1.8A per cell.

Well within the capabilities of these Samsung cells and so low power wise per cell they're not heating up much.