Aspire s7 392 unexpected shutdown on battery power

Hello all,

I really hope I can get some help with this issue. I bought an ACER ultrathin S7 392 about 7 months ago and for the last month it has been shutting down unexpectedly when on battery but not when plugged into the mains. There is no shutdown routine, crash or error message it just loses all power. A second issue which may or may not be related is that sometimes when i attempt to shutdown the unit it restarts instead. ACER support have not been any help at all. I have sent it back to ACER support to fix but I think they just reinstalled windows and when they sent it back they had not fixed the problem. I have since contacted them again and they said it was fine when it left the workshop. From reading the help form it would seem that this is a frequent problem and a major design flaw with the S7 392. It is very disappointing as this laptop was extremely expensive and I spent the extra money so these kinds of problems would not happen. I have tighten the screw on the back to see if this helps but it has not fixed the issue.

Any help would be very much appreciated.

Acer S7 392

Bios 2.09

Windows 8.1