Postscript: It’s started fine since I replaced the battery. So how can you tell? See my first post.
Most places here that sell car batteries have load tester - measures the voltage while applying a simulated heavy load representative of turning the engine over with the starter.
If the battery can’t maintian the voltage while loaded for 30 seconds, it is either shot or on it’s way out and should be replaced. Takes a couple of minutes.
Keep in mind that OEM batteries (and premium brand name batteries) will last longer than “average” batteries. The extra investment today is worth the lack of trouble tomorrow.
I can only see a few scenarios where considering battery replacement a preventive maintenance item would be sensible.
- You have a vehicle where battery failure could be risky in terms of life, limb or money.
-An emergency vehicle would fit in this category.
-If you live in an area with climate extremes or a serious violent crime problem, having a running vehicle may save your life.
-If your vehicle is used to make money. My company has a fleet of service technicians who drive around in full-sized white vans, and depending on product serviced we can charge up to $350 per hour. If one of our guys has two hours of unplanned downtime, that could cost us enough to buy 10 batteries, not to mention breaking quality of service agreements with major clients.
-If your boss will fire you if you’re late one more time, regardless of the excuse. - You just know the battery won’t make it until you sell or junk the car, but you’re reasonably certain that you won’t be driving the car long enough to kill a new battery. I suppose if you had a vehicle that was six years old and you planned on reselling it when it hit 10 years old, you might be in this circumstance.