Correction, before L14 shipped there was information provided that L14 different size barrel plug. L14 comes with 19V and 3,42A power adapter that has a barrel plug size of 4mm outer and 1,7mm inner diameter.
I spent too much time searching on DuckDuckGo and then Google for “BJ size” and “BJ plug” and didn’t find anything useful, only things like BJ’s Wholesale Club, Eaton Type BJ circuit breakers, ball joint, bonding jumper, b***jobs, and BJ Amplifiers.
There are only 3 hits in the world for the Google search [ “BJ size” power brick ] and the top 2 are this thread.
So, what does “BJ” stand for in power adapter context? 
I have both a Librem 15v4 and a Librem 14v1.
To answer the question that the original poster asked in 2020 and was never answered until now: I measured with calipers the Librem 15v4 power brick DC plug: the outside diameter (OD) is 5.41mm (slightly smaller than 5.5mm, which might be the receptacle ID, so probably the nominal number is 5.5) and the inside diameter (ID) is 2.5mm. The insertable length is 12mm. Positive polarity is the inside connector.
So I assume you hit an extra “5” and made a typo with “… standard 55.5/2.5mm BJ plug …” and actually meant “… standard 5.5/2.5mm BJ plug …” That was confusing for a bit.
2 Likes
‘Barrel Jack’ Connector.
3 Likes
Thanks, @Bilhe77 ! I have heard the term “barrel jack” before, but it’s been ages. Not to be confused with another BJ connector, the “Bantam jack”. So many BJs! 
The reason I’m interested in the power brick barrel jack specs is that the original battery (2019-02-27) on my Librem 15v4 was down to half capacity by 2021-01-11, and Purism’s store didn’t (and still doesn’t) have a replacement in stock. So I found one in Hong Kong for $109, bought it 2021-06-06 (and waited 1 month 2 days to get it), and now it’s practically dead.
My Librem 14v1’s battery (bought almost new from friend 2021-12-19) is also practically dead, so I’m giving up on internal batteries and shopping for an external power bank. The one sold in Purism’s shop only outputs on USB-A and USB-C, which would work for the Librem 14v1 but not the Librem 15v4, whose USB-C port only supports data and not USB Power Delivery (USB-PD).
On 2023-04-15 in the forum thread Replacement Librem 15v4 Battery Unavailable, @Mand said, “Aceyoon ACY-L2 20000X external battery (set at 19.5 V) works for me, so I can still use my Librem 15 in trains without power plugs.”
Well, the Aceyoon seems to be out of production now, so I found the Krisdonia Power Bank with a DC output, $120 on Amazon US with a whopping 50,000mAh. It’s too much power to take on planes, but if I need that I’ll buy a smaller one. It comes with a handful of BJs, including the sizes needed by the Librem 15v4 and the Librem 14v1.
Anyone have any experience with it?
2 Likes
Hi, it look’s like a versatile piece of equipment. Just be sure that the charger provided for it will be suitable for your country of residence. It only seem’s to come with UK/EU plugs for it’s own power supply which will be 230v 50Hz rated. It requires DC input: 12V-19V / 2A so possibly you may need to source another charger for it also (worst case scenario) and to find out that BJ’s size also.
Ohh, i was looking at the wrong power bank, the Aceyoon. NVM what i said above, a US one should be fine.
2 Likes
I have heard of adapters so that a computer that only accepts a barrel connector for power can be used with a standard USB-C PD power supply (providing that the power supply has the right voltage and enough total power output). Of course, as you can see, barrel connectors have to be selected carefully for: inner diameter, outer diameter and polarity.
1 Like
Got any URLs for that USB-C PD-to-Barrel Jack adapter? That could come in handy!
1 Like
Krisdonia makes another power bank that appears to have everything the first one does, but with half the battery capacity (25,000mAh) for $90 on Amazon US.
They say it’s “TSA-Approved” but I’m not sure. If you know the mAh rating and the voltage of the battery, you can calculate the Wh. Since the unit outputs from 5-20VDC, I’d guess you’d use the 5V (because the battery is not going to magically have more energy at 20V). Someone who knows this for a fact, please correct me if I’m wrong. I wish battery makers would standardize on Wh, which is a measure of energy that is independent of voltage.
So 5V * 25 Ah = 125 Wh, which does fall within TSA’s limit of up to 2 spare batteries 101-160 Wh per battery.
For the first Krisdonia unit (50,000mAh), 5V * 50Ah = 250 Wh, which indeed is prohibited by the TSA. Might buy the smaller and cheaper one, which is about twice the capacity of the Librem 15v4’s internal battery anyway.
1 Like
e.g. Amazon.com
But note that this is purely illustrative. I didn’t check that that particular ‘cable’ has the right specification for your older laptop. Again, an actual such adapter must have the correct barrel connector specification (inner diameter, outer diameter and polarity) and the correct voltage - and the connected power supply must be capable of producing that voltage and capable of producing sufficient power.
Best case scenario, you could use one USB-C PD mains adapter (or power bank) - and connect it directly to laptop A that takes power via USB-C PD and later on swap it over and connect it via the USB-C PD to barrel connector adapter to laptop B that takes power via a barrel connector.
To be clear … when you power via a barrel connector USB-C PD power negotiation aint going to work. So if you had more than one device that takes power via a barrel connector, you might need more than one USB-C PD to barrel connector adapter, with each adapter chosen to give the right voltage (and of course the barrel connector specifications must also be correct).
2 Likes
Thanks! The exact barrel jack size (5.5mm X 2.5mm) and voltage (20V) came up selected on Amazon. Also, they mention 65W power, which is the output of the power brick that came with my Librem 15v4. Interesting gizmo, and this is the place for gizmos!
1 Like
Use 3.7V not 5V when discussing Li-ion battery packs. The basic cells are 3.7V (for that chemistry) and that is what you should use in converting the mAh rating to Wh. Thus 27Ah will get you to 100Wh (3.7V * 27Ah = 100Wh). You can have multiple 100Wh cells (up to 4?), but 100Wh is all that is allowed without special approval from the airline.
2 Likes
Thanks! For the smaller 25,000mAh Krisdonia power bank, using 3.7V makes the calculation 3.7V * 25Ah = 92.5Wh, which is exact number they advertise. Excellent!
The larger 50,000mAh Krisdonia power bank is still too big for the TSA’s limit of 160Wh (which requires airline approval): 3.7V * 50Ah = 185Wh.
2 Likes