Default [SOLVED][Q] battery charging problem

Solved. The surgery went fine, actually just unplug/replug the battery
and now tablet is charging fine, but only when on. If I turn it off and plug the power cable
I have the onscreen b&w animation of a charging battery but not even 1% increase over the night.
Might consider finding a replacement sooner or later.
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Hi every body

My nexus behaves strangely regarding battery charging, I've tried different cables/chargers same result. I've emptied cache, no result.
Actually here's where I am: When the nexus is plugged with original cable+charger, Battery Monitor says plugged, discharging.
The flow shows a negative mA value. I tried charging the tablet while it's turned off, full night.
Sometimes I managed to get a full charge, sometimes only 5% increase during the whole night.
The usb port seems ok, I can plug it on a computer, copy files both ways, speed is ok. But still no charging.

I've read lots of forum posts concerning battery problems with nexus7, my understanding is that I'm facing
a hardware problem, not software. I have to open it and clean/check the link beetween usb port and the battery charging circuit.
Is there something else I can try before trying surgery?

thx