Hi,
If your UPS works well, and never gave you any problems, your best best is to buy replacement batteries. On most units they're hot swappable, pull out the old ones and replace with the new ones. You don't even need to turn off your UPS.
A lot of vendors will recommend that you throw out your UPS as soon as the batteries are gone, that's a convenient up sell, however not necessary. APC UPSs are very reliable, have no moving parts and can last a very long time. To go out and buy a brand new UPS to get the newest face plate, perhaps isn't financially wise.
:-)
My opinion!
Tony
APC Battery Backup Specialists