Elitebook not charging, no faulty drivers, battery or power adapter

[Merdeper]

First off, I've done all the basic steps of uninstalling ACPI drivers,removing power source, pressing the button for a minute and I've tested with multiple batteries and multiple chargers, both original and aftermarket. I've also tested the batteries and chargers with my other notebooks (I own several Elitebook 840 G2, as well as a first generation version). I can't enter BIOS on this specific laptop, I bought the Elitebooks used in bulk and HP doesn't do unlocks anymore. 

I even tried using Linux to see if it was a problem within Windows, but it isn't. Which was quite a pain to install, without the availability of BIOS settings to allow USB boot. 

The battery isn't charging. The indicator works fine, a solid orange light when plugged in. Also both Windows and Linux show the charger being plugged in. But it simply won't charge the battery. 

My main question is, which part of my laptop is broken?

Edit: it used to work fine for the past 2 years. Battery reports are fine for all batteries that I've tried, and HP Diagnostic shows the batteries to be "Good".

[Merdeper]

I've replaced the motherboard, but kept all the other components the same, and now the charging works. However, I'm still looking for an answer on what exactly may be the cause of my laptop not charging. 

[pbroussard]

The only other thing it would be is the charging circuit on the motherboard.