I purchased this to replace the backup battery in a Verizon FiOS terminal. It was installed 12/27/11, and now the "Replace battery" light is on again, so it lasted only 8.5 months. During that time, AFAIK we never had a power failure, so it was used only for backup. I understand that a back-up battery has a finite lifetime, but I'm unhappy with the 8-month duration of this one.