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Bad Alternator vs Bad Battery Symptoms

Vehicles have interesting systems and components, and the same can be said of their symptoms when they fail. Some of these components even have overlapping failure markers – as is the case between car batteries and alternators. Let’s look at these two components and the similarities/differences in their defect indicators.

Bad alternators and batteries share similar symptoms, such as the battery warning indicator, odd car noises, and erratic starting behaviors. On the contrary, some signs are specific to a given component. For instance, overbright lights could mean an issue with the alternator.

For a more detailed list, here are common bad battery and alternator symptoms:

  1. Activated CEL or Battery Warning Light
  2. Flickering gauges
  3. Cranking or cold-starting issues
  4. Fuzzy or whining sounds
  5. Belt squeals during/after startup or while driving
  6. Dim vs. glaring lights
  7. Sulphuric smell
  8. Jump-starts followed by shutdowns
  9. Warped or swollen battery
  10. Dead battery
  11. Ignition clicks
  12. Corroded, loose, or broken terminals and connectors
  13. General electrical issues

Determining the problem source for each varies in difficulty and partly depends on one’s mechanical inclination and familiarity with telltale signs. The same goes for rectifying identified root causes.

For some of the symptoms, performing a carbon pile alternator test or using a multimeter does the trick. But ultimately, you can outsource addressing these pain points to a trusted mechanic if you are uncomfortable with DIY.

Bad Car Battery vs Alternator Signs

Jeep Wrangler Front Headlights

1. Activated CEL or Battery Warning Light

An illuminated battery warning light can mean a broken alternator belt, a failing alternator, or damaged battery cells. Whether it is steady, flashing, or accompanied by an activated Check Engine Light has nothing to do with specifying which of the three is its underlying cause.

Nonetheless, the battery warning light (whether blinking or not) signifies a potential charging problem in your vehicle. Hence, you will need to test to determine if the problem source is a bad alternator or battery.

If the first two components check out, you may be dealing with a defective voltage regulator or ill-fitted/rusted battery-alternator connections.

In instances where only the Check Engine Light illuminates, it will be best to get fault code readings using a high-spec OBD-II tool like the 2022 Newest FOXWELL NT604 Elite OBD2 Scanner (view on Amazon). The reason is that multiple factors outside the confines of your car’s electrical and charging systems can set off the CEL – not just a failing battery or alternator.

2. Flickering Gauges

Depending on your vehicle make and model, your battery/alternator warning light may display as a battery icon, “ALT,” or “GEN.” More often than not, people assume that this light equates to bad car battery symptoms – not realizing that flickering lights may help pinpoint a specific problem.

Do not get me wrong – flickering for a long time versus flickering almost momentarily are different in what they signify. Normally, a battery warning light that has been flashing for a while would not point to anything in particular. But if the same flickers for a split second before going away, chances are you have an impending alternator problem in its early stages.

This is not to say that split-second blinking lights always mean a compromised alternator. Certain situations – like when it suddenly rains – may cause your alternator output to go beyond its normal range, triggering the same symptom.

It is important to understand how your alternator and other electricals normally operate. This way, you can determine if your car behavior is out of whack.

3. Cranking or Cold-Starting Issues

Whether or not your car engine experiences a temperature drop, repetitive starting difficulties are a cause for concern and often attributed to a starter issue, a failing alternator, or an undercharged battery.

For pre-loved units, it could also happen that challenges with cranking are linked to a battery with an incorrect CCA (Cold Cranking Amps) rating or signal disruptions from the starter system to the ECM.

However, things can be a little bit tricky when dealing with cranking issues. The symptom is intertwined with many other indicators that can trace back to one of the three causes. Any of the three can trigger unusual engine noises, hesitation, oddly behaving lights, and intermittent starting.

Thankfully, some signs lean towards a specific cause more than others. For instance, smoke coming from the hood is better associated with starter issues. The smell of rubber is often part of the signs of a bad alternator. Similarly, an inexplicable electrical draw is almost automatically a sign of a defective battery.

4. Fuzzy or Whining Sounds

Compromised batteries and alternators are associated with this indicator. However, there is a simple trick done by veteran vehicle owners to tell which of the two electrical components is the main culprit.

So the next time you arrive at this crossroad, turn your AM radio to a low number. After which, rev the engine and keep an ear out for noises. Your alternator has likely deteriorated if you hear whining or fuzzy sounds when depressing the accelerator pedal.

Outside of this scenario, you may need to rule out if what is failing is your alternator or car battery.

5. Belt Squeals During/After Startup or While Driving

For this indicator, both the battery and the alternator turn out as the culprit. However, the problem starts with a weak or low-voltage battery. The latter is primarily responsible for putting stress on the alternator, which consequently goes full charge to compensate for the electric load the battery is unable to carry.

Taking on the brunt of the electrical load the vehicle requires to function, the alternator eventually causes the belt to squeal either at startup or while on the road. However, it is important to note that belt slippage is not exclusive to the battery or the alternator.

In most cases, it comes from a mechanical or installation flaw and can be remedied by double-checking the presence of leaks or pulley-tensioner alignment.

6. Dim vs. Glaring Lights

When it comes to lighting as a hint, batteries and alternators are on opposite ends of the spectrum. If your car headlamps are flickering or unusually darker, the problem is with an undercharged or low-voltage battery. If they are overly bright, it is due to the alternator providing the battery inconsistent current supply.

To side with caution, only assume that the problem lies with the battery when dim lights are synchronous with no-crank or no-start issues. After all, the battery is part of your vehicle’s starting system and would naturally cause starting difficulties when defective.

Outside of these scenarios, entertain the idea that other electrical issues could be causing your car’s unpredictable lighting mannerisms.

7. Sulphuric Smell

Rotten egg smells are associated with catalytic converters and any other car component that is sulfur-related (either as a by-product or due to its composition). In the case of batteries and alternators, the smell becomes apparent when the battery overheats, resulting in the inability to hold the charge passed on by the alternator.

In the scenario above, battery overheating produces sulfuric acid or H2SO4 (which eventually converts to Hydrogen Sulfide or H2S). This gas is difficult to detect (being colorless) and is extremely poisonous when inhaled.

As if that were not enough, sulphuric fumes – Hydrogen Sulfide, to be exact – are also flammable and denser than air. It cannot be easily dispersed by merely rolling down your car windows as it may sit below window level inside your cabin.

8. Jump-Starts Followed by Shutdowns

Car Jumper Cables

More of an aftermath than an indicator, jump-starting is often an owner’s recourse when the car battery dies in the middle of nowhere. The act itself does not pinpoint a specific root cause, but what happens after the remedial action does.

If a car engine stays running after a jump-start is performed, the battery is at fault and would likely warrant a replacement soon. Otherwise, the alternator is to be suspected of malfunctioning or failing to deliver sufficient power to the battery.

Note, however, that extreme weather conditions and driver neglect can also lead to a dead battery. Look for warped casings, physical damage to the battery and alternator, and signs of corrosion or leakage.

Many riders find that these indicators are often behind inexplicable battery drain instead of an actual problem with the alternator.

9. Warped or Swollen Battery

Overcharging, deep discharge, or incessant jump-starting eventually leads to a deformed or distended battery. How? Because if you regularly do any of these things, heat and hydrogen gas build up faster than normal – making it harder for the battery to dissipate. Since gas expands when heated, the battery’s outer casing becomes warped or deformed.

Two of the most prevalent causes of this incident are old batteries and overcharging alternators. Perform tests on each to correctly identify the problem source before purchasing a brand-new battery or alternator (view on Amazon).

10. Dead Battery

Both an aftermath and a telltale sign, a dead battery is often brought about by a failing or deteriorated alternator. This is the exact opposite of what happens when the battery takes the brunt of the electrical load your car requires as opposed to acting as a capacitor for the said system (explained in item #5 of this list).

A failing alternator would be unable to supply a constant infusion of electrical power to the car battery. As such, the latter takes up the slack of the former, hastening its otherwise natural degradation process.

When the alternator issue is not spotted or addressed promptly, the repeated compensation by the battery will eventually wear it down to the point of complete failure.

11. Ignition Clicks

Like the above, a rapid clicking sound when turning the ignition is one of the bad battery symptoms stemming from a defective alternator. This sound is non-existent when your battery and alternator are in perfect working condition. However, you can expect to hear ignition clicks when your car battery has insufficient power to crank your engine.

Never attempt to turn your ignition key incessantly in this situation – doing so is futile and detrimental to the alternator, battery, and starting system. To get rid of the noise, check the condition of the three components mentioned, verify that your battery checks out and is fully charged, and then go from there.

12. Corroded, Loose, or Broken Terminals and Connectors

A more common reason behind a dead battery is broken or loose connections. And it can be difficult to arrive at this conclusion without physically checking both.

Because failing alternators and corroded terminals result in a dead battery, a thorough inspection of these components is a must to avoid haphazard remedies and unnecessary repair expenses.

There is a way to determine where the circuitry has broken down – whether on the battery or the alternator end. Typically, compromised alternator connections would be accompanied by overbright lights (an outcome of the alternator producing more energy to overcome resistance from a loose connection or bad wire).

On the other hand, sudden battery drain (plus the absence of overbright lights) can potentially signify flawed battery terminals. It is easier to cross-check if this is the case as car batteries are often accessible, and the powdery blue-green tint on their terminals and connectors are readily visible.

13. General Electrical Issues

Minor electrical issues are tertiary signs of a weak or dying car battery or issues with the alternator’s diode rectifier. The former supplements a vehicle’s charging system, while the latter is responsible for converting AC to DC needed by your car accessories to operate.

If either one of them fails, then you are likely to experience the issues below. Some of these indicators are just specific to a flat battery, while others are bad alternator symptoms:

  • Absence of door lights/chimes
  • Blinking (or non-working) dashboard lights
  • Non-functional sunroof, heated seats, and electronic/power windows
  • Dashboard or radio working sporadically
  • Mobile phones not charging when plugged into auxiliary ports
  • Troublesome or non-working electricals and accessories – for instance, electro-hydraulic lifts on a snow plow like MotoAlliance DENALI 60 inch ATV Plow (view on Amazon)

Bad Alternator vs Bad Battery Life Cycles

While car batteries have an average life expectancy of 2–5 years or up to 62,000 miles, the life cycle of alternators end somewhere between 100,000 and 150,000 miles, according to EVBox and Car Parts. These durations tend to be shorter if the vehicle is subjected to stop-and-go traffic, abuse, driver neglect, or overcharging.

A noteworthy fact about batteries is that they lose at least 5% of their original capacity after the first five years. This means that the older your battery gets, the more accelerated deterioration gets.

Usage aside, below are other factors that may potentially reduce the lifespan of each component:

Battery Alternator
Driving habits
Condition of car charging system
Outside temperature and weather
Applications other than to start the vehicle
Too many electronic accessories
Incorrect CCA or amperage rating Fluid leaks

A best practice I mentioned in another article is replacing your car battery before it reaches its service limit. This way, you can avoid weak car battery symptoms.

Doing so would also help determine bad alternator signs quicker since car battery issues would have already been ruled out.

Conclusion – Bad Alternator vs Bad Battery Symptoms

To recap, below are the most common bad alternator and battery symptoms:

  1. Activated CEL or Battery Warning Light
  2. Flickering gauges
  3. Cranking or cold-starting issues
  4. Fuzzy or whining sounds
  5. Belt squeals during/after startup or while driving
  6. Dim vs. glaring lights
  7. Sulphuric smell
  8. Jump-starts followed by shutdowns
  9. Warped or swollen battery
  10. Dead battery
  11. Ignition clicks
  12. Corroded, loose, or broken terminals and connectors
  13. General electrical issues

Driving with a bad alternator or bad battery is ill-advised, as doing so puts your safety and the integrity of the engine and electrical components at risk.

At best, you may be stranded in the middle of nowhere if your car consequently dies due to a failed alternator or battery. At worst, unaddressed signs of a bad battery or alternator could cause the power steering to malfunction, leaving you without vehicle control on the road.

You would not want to find yourself in either situation – which is why familiarizing yourself with bad alternator and battery symptoms is essential.