If your car battery won’t charge, it could be due to an old, damaged, or dead battery or an alternator problem. Here’s a quick breakdown of the most common causes:
- Bad alternator: Can’t properly recharge the battery while you drive.
- Corroded or loose terminals: Can interfere with the electrical connection.
- Broken or slipping belt: May prevent the alternator from recharging the battery.
- Old or damaged battery: May no longer be able to hold a charge.
- Parasitic drain: Can gradually drain the battery while the car is parked.
How to Diagnose the Problem
- Test the battery voltage: With the engine off, a reading around 12.6V is a useful fully charged reference.
- Test the charging system: With the engine running, the voltage should generally rise as the alternator charges.
These checks can help narrow down the problem, but there’s more to know. Read on for the causes, diagnosis, and ways to fix a car battery that won’t charge.
This Article Contains:
- 10 Reasons Your Car Battery Won’t Charge
- How to Diagnose a Car Battery That Won’t Charge
- What to Do About a Car Battery That Won’t Hold a Charge
- How Much Does It Cost to Fix a Car Battery That Won’t Charge?
- 3 FAQs About a Car Battery That Won’t Charge
10 Reasons Your Car Battery Won’t Charge
Here are the most common causes of a car battery not charging:
1. Faulty Alternator
The alternator recharges the battery while the engine runs. A problem with the voltage regulator can affect how well the alternator charges the battery. Common clues of a bad alternator include a battery or charging-system warning light, dimming headlights, electrical problems, or a vehicle that quickly loses power after a jump-start.
2. Broken or Loose Serpentine Belt
If the serpentine belt becomes worn, frayed, loose, or slips off its pulley, it can prevent the alternator from charging the battery. You may notice squealing, chirping, or slapping sounds when this happens.
3. Corroded or Loose Battery Terminals
Battery cables and terminal connections need to make solid electrical contact. Corrosion, looseness, or damaged cables can interfere with charging and starting. If the battery connections are poor, the battery may be healthy but unable to receive or deliver current properly. You can often spot this battery issue by checking under the hood for corrosion or loose battery terminals.
4. The Battery Is Too Old or Damaged
Battery failure is more likely in damaged or older batteries. When this happens, the battery may be unable to hold or deliver enough charge to start the vehicle. Common signs of a battery charging issue include slow engine cranking, dim lights, frequent jump-starts, or a battery that quickly loses its charge.
5. Parasitic Electrical Drain
A parasitic drain occurs when something continues to use electrical power while the vehicle is parked and the engine is off. Leaving the headlights or interior lights on, or problems with aftermarket accessories or electrical components, can drain the battery. Electrical problems, like a short circuit, can also cause excessive power draw and drain the battery.
If the battery repeatedly dies after the car has been parked, an electrical drain may be the cause.
6. Blown Fuse or Fusible Link
The alternator relies on several electrical circuits to charge the battery. If a blown fuse or fusible link (a section of protected wiring) or a short circuit interrupts the alternator’s electrical circuit, the battery may not receive a charge. A battery warning light or other electrical issues may indicate this problem.
7. Overcharging, Undercharging, or Deep Discharge
A battery that isn’t being adequately recharged can gradually deteriorate. Likewise, repeatedly running it down to very low levels can put additional stress on the battery. The result may be a battery that appears to charge but doesn’t retain enough usable capacity. Signs include frequent jump-starts, slow engine cranking, and rapid loss of charge.
8. Extreme Temperatures
Very hot or cold temperatures can affect a battery’s ability to hold and deliver a charge. You may notice slow engine cranking, difficulty starting, or the battery losing its charge more quickly, particularly after the car has been parked in extreme temperatures.
9. External Battery Charger Issues
Incorrect battery connections, an incompatible charger, or a faulty car battery charger can prevent a battery from charging properly when you’re using an external charger.
This is different from a problem with the vehicle’s own charging system. If the battery charges correctly in the vehicle but not with an external car battery charger, check the charger, its settings, and its connections before assuming the battery has failed.
10. Faulty ECU
An ECU issue can affect the charging system operation, but it is less common than problems with the alternator, battery, belt, or another electrical component.
An ECU issue generally requires professional diagnostic equipment to identify. It shouldn’t be the first assumption when a battery won’t charge.
With the possible causes narrowed down, the next step is figuring out what’s actually causing the problem.
How to Diagnose a Car Battery That Won’t Charge
Follow these checks to help narrow down whether the problem is a battery or charging issue, or another component:
1. Check the Headlights and Other Basic Symptoms
Turn on the headlights and observe their brightness. Dim or non-functioning headlights can indicate a low battery. Slow engine cranking, repeated jump-starts, or a battery that goes flat again soon after driving can indicate a battery or electrical issue.
2. Check the Battery’s Lifespan and Physical Condition
Start by looking for obvious signs of a bad battery, such as cracks, leaks, heavy corrosion, or other damage. If the battery is old or damaged, replacing it with a new battery may be necessary. Battery life typically ranges from 3–5 years, though climate, driving habits, and battery type affect how long it lasts.
3. Test the Battery Voltage With a Voltmeter
If the battery appears low but shows no obvious physical problems, a battery test can help determine its condition. With the engine off, check its voltage using a voltmeter. Connect the red voltmeter lead to the positive battery terminal and the black lead to the negative terminal.
Around 12.6V is a useful reference for a fully charged battery, although readings can vary with temperature, recent charging, and battery condition. A lower reading means the battery isn’t fully charged, but it doesn’t by itself prove the battery is defective.
4. Determine Whether the Battery or Charging System Is the Problem
The next step is to see whether the vehicle is recharging the battery properly. With the engine running, measure the voltage at the battery terminals.
Modern vehicles may use variable or smart-charging systems, so the expected reading varies by vehicle. An abnormal reading can indicate a problem with the charging system, such as a faulty alternator, voltage regulator, wiring, or other related components.
5. When a Basic Voltage Test Isn’t Enough
If the charging system appears to be working but the battery still won’t hold a charge, a proper battery test, such as a load or conductance test, may be needed to assess the battery’s condition. If the test shows the battery can no longer hold a sufficient charge, it may indicate battery failure, and a new battery may be needed.
Once the cause is clear, the appropriate fix will depend on what’s wrong.
What to Do About a Car Battery That Won’t Hold a Charge
Here’s how to address common problems that can leave your battery discharged or unable to hold a charge:
1. Jump-Starting
A jump-start with jumper cables can get the vehicle running when you have a dead battery, but it won’t fix the underlying problem. Follow the manufacturer’s jump-start procedure and safety precautions, and don’t attempt to jump-start a damaged or leaking battery.
Once the vehicle is running, the battery may still need to be charged and tested.
2. Recharge a Flat Battery
If you don’t need to get the vehicle running immediately, a suitable battery charger can restore a flat battery. When the vehicle isn’t driven for extended periods, a smart charger, trickle charger, or battery maintainer can help keep a battery charged.
3. Battery Reconditioning Methods
DIY battery-reconditioning methods involving baking soda, Epsom salt, distilled water, or aspirin are sometimes suggested. Still, they aren’t guaranteed to restore vehicle batteries and aren’t suitable for every battery design.
Lead-acid batteries, including flooded batteries, may be serviceable in some cases, while gel, AGM batteries, as well as other sealed designs shouldn’t be treated like serviceable flooded batteries.
Whether you’ve identified the likely cause or are taking your car to a mechanic for diagnosis and repair, it helps to know what you might expect to pay.
How Much Does It Cost to Fix a Car Battery That Won’t Charge?
The estimates below cover common replacement parts for battery charging problems. Actual costs vary by vehicle, parts, labor, and location.
Here are the average costs, including labor:
- Battery terminal clamp replacement: $26–$240
- Battery cable replacement: $320–$410
- Car battery replacement: $90–$400+
- Alternator replacement: $150–$1,200+
- Serpentine belt replacement: $110–$210
With the causes, checks, and fixes covered, let’s tackle some common questions about car battery issues.
3 FAQs About a Car Battery That Won’t Charge
Here are answers to some common questions about car battery charging problems:
If the battery goes flat mainly while the vehicle is parked, an electrical drain is worth investigating. If it loses charge while the engine is running, the charging system or a bad battery may be the cause.
There isn’t a fixed number of days, but healthy vehicle batteries should normally stay sufficiently charged while a vehicle is parked for at least several days and often much longer.
Battery life can affect how well a battery holds a charge, with older batteries generally losing their ability to hold a charge as effectively as newer batteries. Electrical draw, temperature, and how long the vehicle sits can also affect how quickly its charge drops.
The American Automobile Association (AAA) notes that a car can typically go a month or two without driving before the battery dies. However, this varies considerably depending on the vehicle and battery condition.
Driving can replenish a discharged battery, but how quickly it restores the battery charge depends on the battery’s condition and the charging system. It also won’t fix an underlying alternator, charging system, electrical, or battery problem.
Get Expert Help With Car Battery Charging Issues
If your car battery won’t charge or keeps losing its charge, the cause could be anything from a simple discharge to a faulty alternator, belt, connection, or another charging-system or another battery issue. Identifying the cause is important before replacing parts or attempting a repair.
That’s where AutoNation Mobile Service comes in.
Our mechanics come to you seven days a week, so you can get the help you need without visiting a shop. You’ll also get upfront pricing, and every repair comes backed by a 12-month | 12,000-mile warranty.
Contact us today to have your battery and charging system diagnosed, or to get any other repair your car needs.