Batteries fail in different ways. Sometimes they just die with no warning, sometimes they give you weight issues. I had a bad battery that would engage my blower on high and I could do nothing to change it until the battery was replaced (in in a 4runner but still).
Testing battery voltage is not necessarily indicative of whether it has issues or not, so don't rely on just doing that at home. The battery may not exhibit issues until it's under load, which is what the parts store will test. I recommend you do that.