Posted: Jan 31, 2019
How Do You Know if Your Car Battery Is Bad?
We realize someone reading this may have a bad battery or at least a car that won't start and they're looking for quick answers as to whether or not their battery may be bad and in need of replacement. In the interest of helping those folks quickly, we'll offer this quick advice- try to fully-charge your battery to at least 12.6 volts and have it load-tested. Partially or fully-discharged batteries may not provide accurate test results, so you'll need to at least attempt to fully-charge it before having a load test done.
If you're stuck on the side of the road or trying to get to work, you may not have the luxury of time or access to a battery charger to charge your battery. If that's the case, it might be time to call the roadside assistance service of your choice. However, know that if roadside assistance suspects your battery may be the cause, they'll probably sell you a new one, even if your current battery is only discharged and doesn't really need to be replaced. If you have some time, get your battery on a quality battery charger and take it to an auto parts store to have them load test it for you.
Now, for a longer explanation, we'll use an actual situation that happened to the author, Jim McIlvaine, earlier today. When I hopped in my car this morning, I saw the cold temperatures were still in the area (that's a photograph from my car and that is fahrenheit). I knew that meant batteries were likely failing all over the area, but I didn't think I'd encounter one on my way to the gym. When I arrived in the gym parking lot, I saw a compact Nissan with it's hood up and another vehicle pulling up with jumper cables.
When I approached the car, I saw that it had an auto parts store battery under the hood, so I knew it had been replaced at least once before. I cautioned the owner that using jumper cables was the electrical equivalent of a one-gallon can of gas, that might get you started, but your next stop should probably involve getting your battery fully-charged with a battery charger or you'll likely need another jump. After I went inside, I spoke to the owner of the gym, who indicated the car owner only lived a few minutes away and had to jump-start his car to make it to the gym that morning.
It is a common misconception that alternators can charge batteries. While they could charge a deeply-discharged battery in theory, in reality, most folks don't drive their vehicles long enough and under the ideal conditions for that to occur. Alternator manufacturers will even warn their own customers that alternators are not designed to charge dead batteries and doing so could cause premature alternator failure. The owner of this Nissan probably made a bunch of short trips, that never allowed the alternator to keep the battery properly-maintained, which resulted in the battery getting slowly and deeply-discharged.
Once any battery is discharged below 12.4 volts, sulfation begins to form inside the battery, which diminishes both lifespan and capacity. As we talked about the battery in the Nissan, I decided to run home and get my OPTIMA Digital 1200 and an extension cord to try and recharge the battery. When I connected the charger and measured voltage, it showed 12.6 volts, which would suggest the battery was fully-charged. However, they couldn't get the car started, which also suggested the cold cranking amps might not be what they once were. I went back home and retrieved a portable load tester, to test the battery.
When I hooked up the load tester, it also showed a fully-charged battery and after removing the surface charge, the battery rated at 650CCA only tested at 300CCA and indicated it was bad. At that point, we knew charging the battery any further was futile and the battery needed to be replaced, so we closed the hood and went back inside to warm up. While some folks believe cold weather damages batteries, more damage typically happens in hot temperatures. However, it's the additional strain of trying to start a very cold engine that often manifests the damage that was done to a battery in hotter temperatures.
It's never a bad idea to top off the voltage on your battery overnight with a battery charger and if the weather seems like it's going to take a cold turn, that's the perfect time to plug in your charger. If you're still concerned that your battery might be bad, take it to a battery professional, like your local auto parts store and ask them to load test it for you. If they have a hand-held tester like mine, they can probably do it without even removing the battery from your car and they probably won't charge you to do it.