Power Cover Not Charging 100% 0% 100% ???

So I bought a NOS power cover on ebay and had the same issue as everyone here, having knowledge of li-ion batteries I suspected that the batteries self discharged below the cut off voltage (generally the cut off voltage is 2.2-2.9V/cell) in the charging circuitry that then permits the cells to charge. So with my knowledge of electronics and sense of adventure I managed to gain access to the cells and found that they were discharged down to 1.85V, I applied a small amount of current to each cell raising the cell voltage to about 2.8V, put it all back together and it is now working perfectly. Doing this voids all warranties and as some people will tell you that this is risky if you don't know what you are doing.

So in summary, the problems everyone here are having is due to the cells self discharging and the Battery Management System (BMS) is not allowing the battery to take a charge.

More information regarding "sleeping Li-Ion cells" can be found here:  

http://batteryuniversity.com/learn/article/low\_voltage\_cut\_off

Fantastic! I was just wondering if something like that was possible today. Which leads are to the different cells? Did you just measure the output voltage of the interface on the surface?

Unfortunately no, the only way to gain access is to cut the fabric on the rear cover, under there is an aluminium plate covered in a thin plastic and held down with about 20 screws, once that is lifted there are 4 cells connected in series-parallel.

Ill take some pics of the cover and mark where to cut if you are interested.

Aha, gotchya. If you could post the photos here that would be great. You wouldnt have happened to take photos of the batteries while your's was open did you?

I do wonder what Microsoft will think when they see their products opened up like this

Cut along the red line, see next pic to give you a better idea.

Lift the flap up and you will see this (without the tape), cut out the plastic where the screws are and remove them, cut down the sides of the aluminium and along the bottom.

Flip the aluminium up, and this will expose the 4 batteries, from my measurements the batteries are connected in series/parallel.

DISCLAIMER: do this at your own risk, Li-Ion batteries can be volatile, just check out the pain Samsung are going through with the note 7 at the moment. Please read the link I posted above from battery university.