A Line Mechanic reports he replaced an APU battery and charger that were later found to be 'not' effective for a CRJ-900. Both batteries and battery chargers were identical and passed all operational checks and self-tests.

Narrative

Informed by phone that an APU Battery Charger that I installed on a CRJ-900; was not effective to the aircraft; and (that) I used the wrong maintenance reference. The event happened June 2009. Maintenance Control called out the CRJ-900 APU battery charger caution message. This was in the middle of a very busy push. I went to the aircraft and climb in the aft equipment bay; to see what codes I had on the APU battery charger. The codes were aircraft bus failed and shut down. I went back to the shop to get an APU battery charger and APU battery. When I got back to the shop all the computers were being used. I then asked if someone knew the part number of an APU battery charger for a 900. Someone replied yes; and gave me part number. I went back to parts room to get the battery charger. I then verified the part number that was given to me and compared it to the tag. I removed the old charger and compared it with new charger to make sure I still had the correct charger. The chargers were identical twins. The cannon plug were keyed the same. The bolt pattern was the same. I then installed the APU battery charger and cattery. I then performed all operational checks and self test of the charger. The charger was working properly and no more codes were found. When I exited the aft equipment bay; the aircraft was loaded with passengers and was ready to go. Because of this; I did not want to take a Maintenance delay. I then called the Shop for a reference for the charger and battery. Someone replied on the radio with the reference and I wrote it down in the Logbook. I then returned to the Shop to complete the paperwork in our maintenance tracking system. I realized while doing this report and replaying the events in my head; where I had made some serious mistakes. The first mistake; I should of let the aircraft take the Maintenance delay. By doing so I would not have been in a hurry. The second mistake was; I should have looked up the part in the illustrated parts catalog (IPC) myself; instead of relying on someone else's notes or memory. The third mistake; I should not have compared the charger with themselves. The reason being the Charger being remove might be the wrong part number installed. The fourth mistake; I should of looked up the reference myself; instead of relying on someone else's notes or memory. The reason I did not mention the name of the person who gave the part number and the reference is because ultimate responsibility falls on me.