We've owned a filter system like this for almost 6 years and the battery finally ran out.  It's not replaceable because it is enclosed in the system, but six years is a good long time.  The system flashes a small green blip to indicate that the filter is still working great.  When it flashes a red blip, then you know it's time to change the filter.  That happens about 4 times a year at our house with a family of 5.  It's a wonderful system that delivers great tasting water without the fuss or expense of under-counter systems.  We think it's great and I was glad for the ease of re-purchasing it through Wayfair.