Vlad wrote:
I purchased this unit less then a year ago that comes with two set of
batteries.
One of the batteries failed (short circuit) .I open the unit that
consists of 10 Panasonic batteries and all of them are in short
circuit.
I wonder what makes ALL of them to short circuit.

Although rare in a 1 year old battery, this is usually a sign of
dendrites... whiskers of nickel that grow within the cell as the cell
ages. The dendrites can grow long enough to make a short circuit between
the poles of the cell.