When do you think the battery is a real goner?

OK, this is the situation. I apparently did not close the trunk lid all the way 2 weeks ago and the lamp drained the life out of the battery. The battery is about 5 years old. I tried to jump it but the car won't even turn. You can hear the starter clicked and that was about it. All lights went dead as soon as I disconnected the jumper cable from the other car. So does than mean the battery was at it's last lag? Or did I fry something jumping the car? I frequently heard that the SL is prone to get fry by jumping. Any truth to that? I connected the cable with the other car not turned on. I let the other car ran for a minute before I got into the SL and tried to start it. Was that the right procedure? BTW, it is my '95 SL. Thanks for any input.

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95 R129
04 Infiniti G35.5 BS
10 X204