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USB-C PD battery packs


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Following on from this thread where I did research on USB-C PD (Power Delivery) cables, I've since bought six battery packs for use with my LG Gram 17 and my Samsung NP950XDB.  For various reasons, I'm forced to work on battery for much of the day, so having a battery pack that is both powerful, and USB-C PD compliant, is critical. Further, we've been having quite a few power outages with all the storms here in California, so being able to work on battery has been useful. 


One thing that has become apparent is that my laptops consume less than 10W when performing 'typical' tasks - email correspondence, web browsing, spreadsheet manipulation, etc.  So while the laptop 'might' consume up to 65W theoretically (when working extremely hard AND with the battery needing a charge), I can really get away with 10W or less in 'steady state' - doing 'normal' tasks and starting with an already full battery.  This opens the door to lower powered battery packs, which are smaller/cheaper/lighter. Below, I'll detail the different power packs and their strengths / weaknesses (I'll update this thread with more details), but before I do that, there is a weird problem that I want to bring to people's attention and perhaps find a solution to.  Consider the following: 


Battery packs are devices that can:

  1. deliver a charge to a connected device (eg, a laptop) and
  2. receive a charge from a power source (for example, when re-charging the battery pack). 

Now consider what your laptop is capable of, from a USB-C connector perspective; it can:

  1. receive a charge from an external supply (eg, a wall charger or a battery pack) and
  2. deliver a charge to a connected device, like your phone or tablet


As you can see, both devices can charge each-other. And further, with the introduction of USB-C PD, we have a single port on the laptop that can both receive a charge and deliver a charge.  So when you connect a fully charged battery to your laptop, the battery powers the laptop. But when the battery becomes discharged, it can switch over (under some circumstances) to being charged by the laptop!   This has only happened a few times, but it HAS happened!  In the past, it was happening only when the battery became fully discharged. The particular battery had a decent display that shows charge remaining (%), and also voltage and current draw, and blinks when charging. I noticed it hit zero charge, and then shortly thereafter, the 'charge level' started increasing (and blinking) - and the laptop battery was discharging.   Then last night, I had my laptop connected to a different battery, and the battery was slowly discharging as expected (at around 70% charge level).  But then I noticed the display was blinking, and the charge level was increasing, and my laptop was again discharging!   I think in this case, I wasn't using the laptop and it went to sleep - so stopped drawing any power - and somehow, the laptop and battery re-negotiated power, and the laptop started delivering a charge to the battery.  


It's certainly desirable and expected that your laptop will deliver a charge to a connected device such as a phone or tablet, so I need to find out how to manually control this. Has anyone else run into this situation? 


I'll update this thread with the six batteries that I bought (five different models).  Bottom line is, I can get several hours out of a 20,000 mAh pack, and I can get a full day out of a 40,000 mAh battery pack - assuming my laptop starts out fully charged to begin with. 


Edit To Add: while doing some testing of this situation, I inadvertently ran into another weird behavior.  I plugged my Samsung S10+ Android phone into my Samsung NP950 laptop using a USB-C to USB-C connector, to verify that the laptop delivers power to the phone. It does, as expected.  But - I then put the laptop into 'hibernate' mode, to see if the laptop continued to power the phone; it did not (good!). But then, with the phone still plugged in, I brought the laptop out of hibernate, and ... the laptop is now being charged by the phone! I got a warning on the laptop along the lines of, 'connect a higher powered charger to charge your laptop faster'.  So this is another situation where the 'source' and 'sink' relationship of USB-C devices gets reversed. 




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Following on from the USB-C PD battery idea, I found this device yesterday and had it delivered today. 


For $16, you get a little gizmo that plugs 'in-line' to any USB-C cable and tells you exactly what is going on, 'power' wise. So it tells you what actual voltage is being provided, what current is being drawn, what the resultant wattage is, plus is will accumulate data over time and tell you exactly how many mAh and mWh have been consumed since last reset. This latter feature lets you verify the actual capacity of an external battery pack that may claim 20,000 mAh, for example. 


Here it is, plugged into one of my external battery packs. This battery pack is a BaseUS 100W 20,000 mAh which happens to have its own display of voltage and current: 



Battery pack is saying 20V, 0.3A; new tester is showing 20.25V, 0.351A. The tester also shows that it's been connected for 5m 51s, and has so far passed 152 mAh to the laptop (laptop was fully charged at the time, hence the 7W power consumption). 


Here is the same setup, but this time with another battery pack I bought - 




This (MUCH cheaper) battery pack does not tell you what voltage / current it is currently delivering (the display only shows % battery remaining). The tester here reveals that, even though the battery pack claims to deliver 20V, it's actually only delivering 12V (and my laptop complains when I plug it in - it says something along the lines of 'inadequate power supply ...' - but it still keeps the laptop running and even charges it up, just more slowly). 


Here's another battery pack, a more expensive one, that also claims 20V, and seems to actually deliver that voltage: 




In addition to verifying what voltage / current / etc you are getting from an external battery pack, this device is great because it shows you very clearly 'at a glance' what power is being drawn by the laptop at any given moment, when plugged in.  You can get similar results using 'Nirsoft's "Battery Info View" - but ONLY if you run on battery, and ONLY by consulting the 'log' which is always slightly after the fact.  I guess each 'tool' has it's place; to get good info from this device, you need to first fully charge the laptop's internal battery so that you can assume 'power in = power consumed' (otherwise, the power that is going to charging the battery will skew any measurements). 

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