There are so many variables as to what could be causing your problems its not even funny. Have you tried the basic things, such as driver conflicts, viruses and things like that?

That laptop should run Supreme Commander just fine. I have a 9300 and I can run supreme commander on it alright.

If you think your memory is causing the problem, run memtest to check it out. If any errors get reported then your ram is the problem, if no errors then your ram is fine.

As for the battery... is your laptop still under warranty? If so, make Dell replace the battery.

IMO there is no need to replace your laptop. Worst comes to worst, reload the OS and that should fix any software problems.