Unfortunately, you did. Batteries need to be used occasionally. After two years of disuse, the battery likely discharged to the point where it can't recharge.
A trick I saw on the net once was the pop the battery in and out a few times (like 10 or so). The idea was that the power from the PowerBook would act as a "jump start" to the battery. This was for the Pismo/Lombard machines and I have no proof it ever worked, but you may as well try it.
Good luck.