Did you try to force the charging mode with flasher?
When battery is totally flat the device cannot even start charging as it requires it to start up a little bit to run the charging algorithm.

Start flasher like you would flash the device, and it should say that charge is not enough to fo it, as it is requires to have 11% charge for flashing.
Then the flasher starts to force-charge it, and it will slowly show the charge rising, percent by percent. When it reaches 9% or 10% or so, before it is enough to start flashing, disconnect it and plug to wall charger to charge it to full