If a battery has not shown signs of failure or weakness, I usually change mine proactively at about 8 years age. You can run a check of the open circuit voltage after a full charge and rest period. The voltage is measured, then you consult a chart which will give you an indication of the percent capacity remaining.
You can also do a load test to assess battery condition.
Since you carry a booster, I'd suggest waiting until signs of battery failure before changing it, unless you're planning on taking a trip to the boonies.
Many people might report far shorter average battery life than what I experience, but I think cold winter storage extends the life of mine. Batteries living in hot climates do not last as long, and in extreme heat they don't last long at all. So, if you live in a hot climate, adjust your battery life expectations accordingly.