I don’t think there is any way to answer your question because it depends on the individual dock. I would expect a decent dock to choose the latter option. The only way to know for sure is, on the Librem 5 side, issue the appropriate shell command(s), or, for either USB-C connection, use a USB-C power meter.
Note that the Librem 5 will not typically get 3A because it won’t typically ask for that much or draw that much - but let’s take that as what the potential exists to deliver in the second scenario.
The maximum amount that can be charged into the L5’s battery is 5 volts and 1.6 amps (8 watts), but in my charging tests, I found that the L5 could use a varying amount of power in addition to that to operate itself. Unlike most phones, the L5 can operate directly from the power it receives from the USB-C port, so it doesn’t need a battery if it is plugged in.
I did some charging tests with the L5USA and a USB power meter last year, which might interest you:
Btw. I am not sure that it is clear, that I am not meaning charging only, but also the total current that Librem 5 consumes. So this means running the device plus charging the battery.
So what I get until now is the following:
Librem 5 only accepts 5V at the moment.
There is evidence that Librem 5 consumes over 5V 2A.
There are statements (official?) that the battery can be charged at up to 5V 1,6A.
This would mean that everything that would be above would go for running the phone and as the phone needs different amount of power depending on the load this would explain the fluctuations up to 5V 2,5A
Now what I still don’t get is the following:
Librem 5 will negotiate with the docking station 5V.
Does this means that the docking station will have to negotiate 5V with the power supply as well or could the input and output voltages of the docking station be different?
Irvinewade writes that it will depend on the docking station itself but I have not found any evidence on the internet that the case exists in which the negotiated voltage for the input and output will be different. I don’t know also how do people interpret the “Pass Through” charging.
This question is very important for understanding because if the docking station does need to negotiate 5V with the power supply than a power supply like the 5V 2A / 20V 3,25V I have, would be total crap for convergence mode. The original power supply 5V 3A would also be insufficient for a great convergence experience. So one has to not only look for a proper docking station, but also for a proper power supply capable of something like 5V 5A or 5V 6A.
The world would have been too easy if there was an original Librem 5 docking station with power supply Now I understand why many computer brands are able to sell docking stations for several hundred USD.
So if you have the Lenovo power supply and you have a docking station, why not just connect it up and ask the Librem 5 what it is getting? With the supplied charger, the Librem 5 reports PD negotiation of 5V 3A max.
First, thank you @Hristo for asking very qualified/related question (as made my older brain awake) and as second (and equally very important) thank you @irvinewade for getting/posting here your qualified/related answer:
As third I’m already very tired for today but needed to post at least above screenshot (×2):
SB-AC16-TCUS, USB-PD Type-C 5.0V/3.0A, 15W, DCP based power supply, directly charging L5;
Anker A2029, USB-PD Type-C, 60W, DCP based power supply, directly charging L5;
PD-014, USB-PD Type-C, 18W, distributed power supply, directly charging L5;
AENZR AZ2406, getting power from SB-AC16-TCUS (15W) power pass-through toward L5, all good (post #15 in this thread);
AENZR AZ2406, getting power from Anker A2029 (60W), power pass-through toward L5 is not usable 0.4790A (not good at all);
AENZR AZ2406, getting power from PD-014 (18W), power pass-through toward L5 is not usable 0.4790A (not good at all).
Yes, 5. and 6. are having red LED light on but in terms of L5 battery actually meaningless (IMO). Yet, I do think that this is a great finding anyway. Therefore thanks on both of you repeatedly! @Hristo, now is your turn again, please explain what you actually discovered for all of us here (relating to your recent posts). My hint would be: 1500000 (marked green within second screenshot above):
I tried 3 different phone chargers capable of delivering 5V 3A (Purism, Sony, and Samsung). All 3 negotiated 5V 3A.
I tried the 65W charger of the Lenovo notebook which is designated as 5V 2A, 9V 2A, 15V 3A, 20V 3,25A.
Surprise. The command returned negotiated 5V 3A even though the power supply states 5V 2A. It would be interesting to measure real consumption under max load to see if it really goes above 5V 2A. I don’t have instruments to do the measure.
Then I used the following docking station: https://www.amazon.de/dp/B09Q5SRZTD/
I tried all 4 power supplies from above through this dock and Librem 5 showed in all 4 cases just 5V 0,5A
Then I tried the Lenovo Thinkpad Hybrid USB-C with USB-A dock Type: 40AF. This dock has its own non USB-C power supply 20V 6,25A.
Librem 5 showed negotiated 5V 3A but unfortunately display signal is not working. Maybe it is due to the sticker “Display Link”. Really a pity because this docking station would have been perfect if displays were working as it has plenty of USB ports and both HDMI and DP ports so it would have been really convenient.
Conclusion:
The huge Lenovo docking station with 20V input can indeed negotiate 5V output. But it is also much larger than the pocket docks we discuss in most of the cases and I am not sure if they also have the possibility to convert the voltage from 20V to 5V.
In short (while someone already waiting for me), please try the following combo with your Librem 5 (only 5V/2.4A or only 5V/3A power supplies should, as I’m expecting, charge Librem 5 connected to the compliant docking station up to more than enough/adequate 5V/1.5A , while no other voltage negotiated, as only 5V present):
Another observation.
I have a display that accepts either HDMI or USB-C as video input.
When I connect Librem 5 directly to this display via USB-C to USB-C, the display works.
When I use any of the 2 docks in between, the video does not work.
(Librem 5 - USB C USB C - Dock - USB C USB C - Display)
I think that might be expected. If the dock has HDMI out then I think it will forward the video to HDMI when the input USB-C is in DisplayPort altmode. Of course I could be wrong. You could find a dock that has enough functionality to forward the video via a USB-C output. However it is not only about the dock’s handling of video, it is also about how the dock reports things to the host.
If you want to investigate then you will need to use lsusb with a non-working dock and with a working dock - and for us you will need to clarify whether the docks have HDMI out.
As I understand it, with the present charging settings, you will struggle to draw much more than 2A anyway. While a USB-C power meter would be the right equipment to measure for sure, you may not need it.
If the negotiation is for 3A max but in reality it is limited to 2A and you can force the draw to exceed 2A then I guess something will be observable on the Librem 5 i.e. either something bad happens due to insufficient power (shutdown? crash?) or battery charging will be limited (which you should be able to see with the right cat /sys/... incantation).
Check POWER_SUPPLY_USB_TYPE to see whether you got PD or C (or something else).
500 mA, as the standard USB 2.0 maximum, is what you will get when connected to a vanilla USB port that does not have PD (or does have PD but negotiation failed).
Regarding overheating while charging: can you help to mitigate this issue by limiting the amount of current during charging? IE: 5v @ 500 mA? What is the lowest amperage that the phone needs to successfully charge?
For me this makes no sense because Librem 5 can work without battery if it gets enough power. So for me the goal is that it runs without using the battery when in convergence mode. If the battery is kept charged and bypassed then the battery will heat less than if it constantly discharges/charges, or am I wrong?
This is also my motivation why I want to get as much as possible power through the dock to Librem 5. So that it gets enough without having to suck from the battery.
I am definitely curious to learn about the consumption of Librem 5 if you want to run it without any limitations and without a battery. But honestly I doubt that it consumes so little energy.
Raspberry Pi 4 requires a 5V 3A power supply and when using less power you get a warning message, that the system gets too little power and this could cause data loss.
Do you believe that Librem 5 with LTE modem and WiFi is going to consume 6 times less or even twice less? I doubt it. But this would be very very very interesting to find out.
I think if you want to prioritise running the device and not charging and the battery level is low enough that it would charge if the Librem 5 is receiving power from the USB-C port then you would have to override the default behaviour with magic incantations.
Let us say I take the battery out and use a dock set-up that delivers 5V 1,5A like the maximum achieved in the tests of Quarnero. Will Librem 5 warn me that it does not get enough before some damage / data loss occurs?
I don’t want to damage the device.
I compare it with Raspberry Pi 4 in my head.
Librem 5 has a display while RPi doesn’t.
Librem 5 has an LTE modem while RPi doesn’t.
Librem 5 has a WiFi module that is not part of the SoC and is more capable than the built in WiFi of the RPi which does not necessarily means that it needs more power, but I GUESS it needs.
At least because of these 3 factors I would GUESS that Librem 5 needs more juice under average load and under full load compared to average load and full load of RPi4.
It would be nice if we had an official statement on what is sufficient for running Librem 5 without a battery and for example for a hot swap of the battery.
Now I understand why many computer brands are able to sell docking stations for several hundred USD. 
