Nowadays it is rare to find a car battery that lasts for longer than three years or so, mainly because car batteries have reached the limits of their development potential. The demands of modern automotive electrical systems are such that batteries work much harder now than they have ever done in the past, and unless completely new battery technology is developed, all of us will at some point get that sinking feeling when the engine suddenly will not crank- just as we are leaving for an important meeting across town.
So how do you know when your battery is about to die on you? Some symptoms are not clear cut, since there are other issues that can mimic the symptoms of a flat or defective battery, so read on, and we will tell you how to diagnose a defective battery.
Slow Engine Cranking Speed
Slow cranking speeds can be caused by a defective starter motor, and/or poor ground connections, but if the engine cranks slowly, one way to test the battery is to let go of the key, and to switch on the wipers and the headlights.
If the wipers work noticeably slower than usual, or if the headlights appear markedly dimmer than usual, the battery is most likely defective.
If the lights and wipers work normally, the cause of the slow cranking is more likely to be:
- A defective starter motor
- Poor ground connections between the engine and the body work on the one hand,
- Poor ground connection between the battery and the engine.
However, in some cases, the engine might start to crank fast, but gradually slows down as the battery fails. This is a sure sign of a defective battery, and most other possible causes can be ruled out.
Illuminated CHECK ENGINE Light
Even though the car might start normally, low battery voltages can trigger the CHECK ENGINE light. Most critical systems that collectively make up the Engine Management System require full battery voltages to work, and even though they may work, they will not work at peak efficiency, and the fact that they receive less than a full battery charge will register on the OBD system, which will trigger the light.
Some symptoms of low battery voltages include rough, or erratic idling, misfiring at high engine speeds, and sporadic illumination of various warning lights, slow wiper speeds, malfunctions of the alarm, security, and central locking systems, erratic instrument readings, and even frequent, and unpredictable stalling of the engine.
Moreover, low input voltages can damage sensitive components, which can add huge amounts to the replacement cost of the battery, so never ignore any warning lights, even though the car may appear to be functioning satisfactorily, since not all cars will exhibit outward signs and symptoms of low battery voltages.
The only reliable way to confirm or eliminate the battery as the faulty component is to have a comprehensive diagnostic check performed, since even professional mechanics often overlook the battery as a possible cause of the illuminated battery light.
Frequent Jump Starts Required
Batteries can fail without warning, so if you require a jump start in the afternoon when the car started normally in the morning, the battery is very likely at fault, especially if it is older than two years.
Another indicator of a defective battery is if the car will not start in the morning during cold spells, but starts in later in the day when temperatures have risen somewhat. The reason for this is that batteries are less efficient at low temperatures than at higher temperatures, which is why your battery has a “cold cranking capacity”.
In new batteries, this refers to the amount of power a battery can deliver at low temperatures, but as a battery ages, this capacity diminishes significantly, until it reaches the point where it does not work at all at low temperatures. The only reliable way to determine if this is the case is to have a “draw” test performed. Most battery centers will perform this test at no charge, provided you buy the replacement battery from them.
Smell of Battery Acid is Present
If a battery has internal short circuit, the electrolyte, which is a mixture of sulfuric acid and distilled water, starts to boil, hence the characteristic smell of sulfur around the battery. However, a defective alternator can also cause the electrolyte to boil when it overcharges the battery, which will not necessarily trigger the CHECK ENGINE light, but it will eventually destroy the battery.
Nonetheless, even slight overcharging will damage the battery, which is why it is important to have the cause of the “rotten egg” smell investigated immediately it becomes apparent, or noticeable. Do NOT ignore this symptom, because a boiling battery generates large volumes of highly flammable hydrogen gas, which can produce potentially devastating explosions in the engine compartment, or worse, in the passenger compartment if the battery is located in the car, such as in many German cars.
Moreover, an overcharging alternator will not only damage the battery; it will almost certainly damage, and possibly destroy sensitive electronic components as well.
Battery Will Not Hold a Charge
There are several reasons why a battery will not hold a charge, such as defects in the electrical system that continually drains the battery over a period of hours to the point where it will not be able to start a car. However, other reasons include internal short circuits in the battery, or overcharging of the battery over extended periods of time, which causes the battery case to swell, deform, or form bulges on the sides of the case. Batteries that are damaged in this way will also run down in a matter of a few hours, and it may not be possible to recharge them when they do.
If this type of damage occurs, the only remedy is to replace the battery, and to have the car’s charging system checked at the same time to either confirm or eliminate overcharging as the cause of the battery failure. A thorough inspection of the car’s electrical system is also a good idea, because it will confirm or eliminate serious short circuits that could damage the replacement battery as well.