Two 796s with starting problems in one day? Must be something in the water! (See jonzi's thread.)
You say the the oil light comes on - did it do this before it cut out or only after the engine stopped? If it illuminated while running then it needs investigating but if it only comes on after the motor's stopped, there's no problem - that's what it's meant to do.
As for the battery, have you checked the voltage on the dash (pushing the mode rocker switch forward once should display the voltage on the dash (at least it does on the Evo).
Nine years is certainly old for a battery so it could well need replacing. Have you seen any error messages on the dash e.g. 0008 r.SW and/or 0005 r.SW?
It's always a good idea to check both battery terminals are tight and clean plus the main earth connector and the line to the starter solenoid. Also check that the injector relay is pushed fully home. Mine worked its way loose and caused similar symptoms to yours.
Good luck!
The injector relay is number 15 on this diagram:
And lives on the battery box (number 6 on this diagram.
