After 3 years of good services, my Sony Vaio VGN-SZ1HP's battery just died.
The laptop would only work connected to mains and would not detect the existence of a battery.
I decided to acquire an original Sony Vaio battery to ensure I would not experience any problems with compatibility and especially, to ensure it was totally safe.
The original Sony Vaio VGP-BPS2C proved the right choice, it worked perfectly just like when it was new.
The only down point is it's price but...