[Nexus 7 Q&A, Help & Troubleshooting] mr.crabs!:
I have done some further investigation this evening on my son's tablet with some success.

With his current hardware and with the tablet switched on it was drawing 0.46A from the OEM nexus charger (tried two known good chargers with same results), and 0.7A from my Samsung tablet charger. Both chargers are 5V 2A output. This resulted in very slow charging.

I then tried changing the USB port assembly with two known good ports. Instantly the charging current jumped to 0.81A when using both chargers. I replaced the old charge port assembly and tried again. It was now also pulling 0.81A. I figured this could have been due to either oxidised contacts on the charge port assembly to mainboard flex or on the connector on the charge assembly which this flex fits into. After cleaning both parts it is reliably pulling 0.81A all the time. This is an improvement.

Now I test my own nexus 7 which charges at a rate of about 30-35% per hour and see what it is pulling. Also 0.81A. Feeling happy I have fixed my son's tablet I leave it on charge for an hour. It increases charge by around 18-20%. Not bad. I realise charge progresses in a curved charge graph pattern (i.e is not linear progress) but this is just comparatively speaking. The level of charge in the batteries in both cases was approximately the same and so I can draw that comparison. Besides, having had a lot of these nexus 7s I know roughly what rate it should charge under normal circumstances. Also, android version and kernel are exactly the same on both.

So, I carry on trying to find the source of the reduced rate of charge despite the same current being pulled by both tablets. I try:

(IS IT THE CHARGE ASSEMBLY?):

》Rewet the 5 pins on the back of the micro usb port where they connect to the charge port assembly board.

》Replaced whole assembly again.

(IS IT THE CHARGE FLEX?):

》Cleaning the end of the charge flex where it connects to the CHARGE PORT ASSEMBLY and it's corresponding connector.

》Cleaning the end of the charge flex where it connects to the MAIN BOARD and it's corresponding board connector.

》Changing the charge flex for a known good flex.

(IS IT THE BATTERY?):

》Changing for known good battery.

》Cleaning the battery connector pins on the main board.

》Rewetting battery connector solder points on main board.

None of the above made any difference to the amount of current being drawn whilst charging. HOWEVER, the above could be a solution to your issue depending upon where the fault lies. This is surely why there are so many conflicting methods to solve this issue and why some work for some people and not others. If you have tried the above and no improvement then you are at the same point as I am.

Being a scientist by trade this logical and methodical elimination of possibilities leads me to believe that it can now only be one of two things remaining (unless anyone else has any thoughts?):

》》Hardware fault somewhere else on the circuit board within the charging circuit of the tablet (needle in a haystack?).

OR

》》Firmware/Kernel issue. I have heard that some kernels allow for a so called "fast charge" scenario which appears to help. As both my tablets have the exact same firmware and kernel on them then the only way I can see the kernel to be the problem is if the two tablets have slightly different hardware inside them (known to occur with tablet manufacturing even within the same model number), and the kernel is not functioning the same in the two instances.

The latter is my next port of call.

I did notice when I turned my son's tablet back on that for a period of a few minutes it was charging and pulling 1.10A before dropping back to 0.81A. Is this the kernel causing this...?

My mother in law's nexus does the same thing. It has same firmware and kernel. I have used this firmware/Kernel combo many times. It does not always result in a slow charging tablet. Maybe this is hardware version related.

I'll let you know when I've had a chance to investigate further. Sorry for the long winded post. Just brain dumping. Feel free to suggest anything. We gotta sort this out once and for all even if it's to say "sod it, I can't do anything else"

Thanks.