Mine usually lasy at least 7 years but I use a CTEK conditioner. Halfords supplied the last but one battery & it was 8 years old & going strong when I sold the car.
Sounds about right. One thing worth mentioning based on two vehicles I don't use everyday is that they will always take a noticeable current when put on charger, even if last journey was a long one leaving battery fully charged.
A typical new lead/acid battery will loose 5% of its charge/month if left and this will only worsen with age. This before any tiny static loads are taken into account.
