I purchased a Battery (AJC-D7S) last year for my Emergency Light and it will not charge anymore. Is that about the average time for one of these batteries to fail?

That seems very short, even for an improperly- maintained battery.

In general, a SLA battery will last between 3 and 5 years, depending on factors such as charging, cycling, complete discharges, operating temperature, and how the batteries are maintained. Your batteries should be tested regularly as per your local requirements. Our batteries have a 12-month warranty. If you are within this time period, please contact our customer service to arrange for a replacement.