How Do I Know When My Car Battery Needs Replacing?

Tips & Support
OPTIMA Batteries
Bowling Green, KY
There's a lot of bad information floating around on the Internet about replacing car batteries from very questionable sources. We'll try to set the record straight for you on how you can determine if it's time to replace your car battery, by dispelling some common myths about what are considered "signs" that a battery is failing.
Myth #1- Your engine is starting slowly
Many batteries returned under warranty are just deeply-discharged and work fine, once they are properly-recharged. If you notice your engine is starting slowly, the first thing you should do is check your battery voltage (it should be at least 12.6 volts) and charge your battery, if necessary. If you don't have a volt meter or a battery charger, you may want to get them, as they can save you a lot of money in the long run. Either one of OPTIMA's battery chargers can also measure battery voltage on any 12-volt lead-acid battery with one-touch functionality and are very easy to use. If your engine is still starting slowly after charging your battery, have it checked (load-tested) at a quality auto parts retailer. Many will offer this service for free and this is the best method of determining if your battery needs to be replaced.
Myth #2- Dim lights and/or electrical issues
Once your engine is started, electrical demand is generally handled by the vehicle's charging system (alternator). If you notice your lights are dimmer or other electrical issues as you drive, you'll want to check the output of your alternator at your battery terminals with a voltmeter. It should be in the range of about 13.7-14.7 volts, but if it's much lower than that, then there's a good chance you have an electrical issue not related to your battery. It could be an alternator that needs to be replaced, but it could also be a loose or worn-out belt that is making it hard for the alternator to provide adequate power. If your battery voltage is also down, try charging your battery with a battery charger. If it charges up fine and holds voltage overnight (or for 12-24 hours), but starts dropping voltage again as you drive your vehicle, you definitely have an electrical issue, but it's probably not the battery.
Myth #3- The check engine light is on
Depending on the vehicle, an illuminated check engine light could literally be anything under the hood. The last thing you want to do is start throwing parts at your car to try and make a warning light go out. If you're concerned that it might be the battery, check the voltage level (at least 12.6V), charge it with a battery charger if needed and then have it load-tested for at a quality auto parts retailer. Those are all free options that should be explored before you spend any money. Once those are exhausted, you should have someone (like a trustworthy & knowledgeable auto technician) read the code that triggered the check engine light, to find out exactly what your car is trying to communicate is wrong with it.
Myth #4- A bad smell
Bad smells can be a lot of things, like a failing catalytic converter or roadkill stuck somewhere in your car. However, if you notice a rotten egg or sulfur smell coming from the battery, your battery could be venting flammable and toxic fumes (and also possibly acid). In many cases, this odor occurs because a battery is being severely overcharged. Once again, we'd recommend checking battery voltage (at least 12.6V) and alternator output (~13.7-14.7V). If you notice the alternator is charging your battery at a much higher rate than 14.7 volts, then you should have your charging system checked by a trustworthy and knowledgeable auto technician as soon as possible.
Myth #5- Corroded terminals or connectors
OPTIMA Batteries are sealed, so you'll never need to worry about corrosion at your battery terminals. If that's the case and all car batteries have finite lifespans, how can you expect corroded battery terminals will indicate your OPTIMA battery needs to be replaced if they never happen? On other vehicles with regular flooded lead-acid batteries, if you see corrosion forming around your terminals, it doesn't mean your battery needs to be replaced, but it does mean there is probably significant resistance building up around that connection, which can make it harder for your battery to accept and deliver current. Clean those connectors and battery terminals with a wire brush and a solution of one tablespoon of baking soda mixed in a cup of hot water. Then check battery voltage (at least 12.6V), charge if needed and have it load-tested for free at any quality auto parts retailer. If it does need to be replaced, consider a sealed OPTIMA battery, so you won't have to clean up that mess in the future.
Myth #6- Bulging battery case
The two most-common reasons traditional "black box" battery cases start to bulge is because of sulfation building up in the plates, forcing them to expand or because a battery is being (or has been) severely-overcharged. Neither scenario necessarily means your battery needs to be replaced right away, but as you can see from the other answers, you should do some checking. Verify the battery is fully-charged (at least 12.6V) and the charging system is functioning properly (~13.7-14.7V). Then, take the battery to a quality auto parts store and have it load-tested free of charge. If it holds voltage and passes a load test, have a trustworthy & knowledgeable auto technician take a closer look at your electrical system, to see what might be causing your battery case to bulge.
Myth #7- An old battery
We definitely want your business, but not before we need it. The definition of what constitutes an "old" battery can vary significantly. OPTIMA batteries can last up to three times as long as a traditional flooded battery, so someone in the desert Southwest, who typically doesn't see three years out of a typical flooded lead-acid battery before it fails may consider a two-year old battery to be "old." On the other hand, someone who lives in a very mild climate, like San Diego, may see seven or eight years out of a battery before it fails, so two years old is close to brand-new for them. If they are using an OPTIMA battery, they may start bragging to their friends about their ten-year old OPTIMA battery still working great. Regardless of the age of your battery, it's a good idea to keep it fully-charged (at least 12.6V) to maximize both performance and lifespan. If you've had your battery for what seems like a long time for you and you are concerned that it might be on it's way out, fully-charge it and have it load-tested for free at a quality auto parts store before you decide if it needs to be replaced.
Whether you have an OPTIMA battery or a traditional flooded lead-acid battery, the best thing you can do to maximize battery performance and lifespan is to keep your battery fully-charged to at least 12.6 volts, whenever possible. We've offered advice about battery charging to dispel a lot of myths about battery replacement, because the root of many (but not all) of these issues is just a discharged battery and not one that needs to be replaced. In some cases, there may not be anything wrong with the battery or the vehicle's charging system, but a car just isn't used often enough or driven for long enough periods of time to allow the vehicle's charging system to maintain adequate voltage in the battery. If that's the case, regular use of a quality battery charger or maintainer can go a long way toward allowing your battery to go a long way before it really does need to be replaced.