Most newer units have something like a 5 year battery life, and a 10-12 year 'service' life.

Depending on manufacturer, make and model there are self tests; some will support a satellite self test. These will eat some battery, but are recommended from time to time (some units support hundreds of self tests over the 5 year battery life).

Battery replacement can require manufacturer involvement, and is recommended when you hit the battery life mark (5 years or whatever).

I'm getting close to needing a battery changeout.

Also note there is another difference: some PLBs have built in GPS units, these pinpoint your location better than ones that do not (but also cost more). They transmit your location to the satellite; the other varients depend on the satellites being able to triangulate you, plus they transmit (for a day or two) a local signal for the searchers to home in on.