MacBook Air Display Resolution Resets

My first generation MacBook Air intermittently resets display resolution to low when waking it from standby mode. Works fine when booting from a restart, but not on waking. Resolution is normally set to 1280 x 800. Will intermittently reset to 800 x 600. Is there a cmos battery that may need to be replaced, or some other possibility? Already reinstalled the OS. Running OS X 10.6.8