The number on the front of your device is not your model number!
You will need to look on the back of the APC unit for a sticker with the serial number. This sticker will also have the model number listed. Below is an example:
In this case, the model number is "BN1500M2" and can be used to search for replacement batteries or support on the APC website.
Per APC, the model number on the battery itself should NOT be used.
You can order replacement batteries and more here.