Several years ago, my father bought himself a Saab convertible for his Monday-morning commute. (At the time, he was actually commuting to work a few days a week, now he's down to just Monday mornings.)
Sometime last year, it started draining its battery in less than a week of standby time, so the once-a-week drive was no longer enough, and he keeps it on a trickle charger.
I was over there this morning, and the latest development was: it don't work no more. Doesn't respond to the (electronic) key. Everything remains locked (except for the doors, which he hasn't been in the habit of locking).
Battery voltage is 13.25 while on the charger, dribbling off quite a bit faster than I'd normally expect when the charger is removed, but perhaps good enough.
Has the security computer gotten out of sync with the transponder in the key? Or has it just temporarily misplaced its mind? What happens if we disconnect the battery, wait a few minutes, reconnect it, and try again?
Or - happy thought! - surely there's a second key. Does that work? He goes off to fetch the spare key. Voila! We have a started car. Now... how to re-introduce the first key, given that we have one-each working key in hand? Apparently the local Saab dealership is long gone; who else would know how to do this?
Meanwhile, we'd both been trying to figure out how to extricate the metallic backup key (doors only, if memory serves) from the bulky plastic housing of the eKey. I finally apply enough force to dislodge the one from the key I'm holding (the not-working one).
There's a little notch that looks like it's for prying the housing open, perhaps using the tip of the metallic key. So I do that.
There's a CR2032 coin cell in there. Key's prolly just got a dead battery is all.
Ya know, in my day ya never hadda worry about your key's battery going dead!