If it's the Intersolar vent as delivered from Cobra, it's likely
"D.E.D."
The 4" Nicro Day/Night vent with C-cell NiMH battery works very
well. You'll just need to drill 3 new mounting holes and plug the old
ones if replacing an Intersolar vent.
If the battery is completely dead, the Nicro may not work. If the
push-button switch inside (not everyone knows it's there) is in the
OFF position, it won't do much either.
The Nicro is available from most gliding suppliers or marine
suppliers.
Jim