How long is the battery life of a UPS? I have a UPS that is 3 years old, is the battery basically useless? Is it expensive to replace the batteries?

The brand and size of the battery has a certain relationship, UPS power supply inside the built-in battery, basically with a three years or so will not work, UPS external battery pack batteries, 65AH above the common brand 3-5 years, joint venture brand 6-8 years. UPS component batteries can be said to be more expensive, the longer the time delay, the more expensive the price.