Can You Overcharge a Car Battery?

Car batteries should go through thousands of charging cycles before they die. To keep your battery alive for longer, you need to exercise good battery maintenance. First, you need to know how a car battery works and how to avoid overcharging it.

Regular Car Battery Charging

If your car is running well, then it means that the alternator is doing its job. Most vehicles will have a light to tell you if there is a problem with the battery. Some cars also have voltage indicators, where you can see the health of the battery in real-time.

What Causes a Car Battery to Overcharge?

Overcharging can end the battery not being able to hold any charge or even melting. There are a few reasons why a car battery may overcharge, and spotting them early can save your engine’s performance.

Can you overcharge a car battery?

Trickle Chargers

Trickle chargers are good for storing your battery and for cold start-ups. But you need to pay attention to the voltage the charger is set at if you are going to leave it attached for weeks or months.

The best trickle chargers keep the amperage low and turn off when they recognize the battery has a full charge. Some chargers will charge with more amperage, which is fine for a couple of days to bring a battery back to life.

Malfunctioning Alternator

When your car’s engine is running, it should spin the alternator, generating a voltage below 14.8 volts, and send it to the battery. A typical car battery wants to charge between 13.6 and 14.6 volts. Above this voltage, you can overheat the battery and damage it.

Readings below 13.5 volts can mean that the battery is having to give out more energy than it is receiving from the alternator. Either way, abnormal voltages will damage the battery. You are also going to notice things like the headlights dimming or fluctuating.

One sign that the alternator is dying is the engine being unable to speed up. If an alternator breaks, it will not be able to generate enough power to pump fuel to the engine. Even if the battery is fine, it will flatten fast without the power from the alternator.

Indications That a Battery Is Fully Charged

You are going to notice that your car will start much easier when the battery has a full charge. Written on the case of the battery is 12 volts, which is the voltage it sends out to the electronics. Though to charge from your car, the battery needs around 13 to 14 volts.

If your vehicle has a voltage indicator, the battery should read around 12.6 volts with full charge when the engine is off. Most car chargers have voltmeters on them — you need to see what the battery voltage is when the charger is OFF.

> 6 Reasons your car battery is dying 

How to Check for Overcharging

Batteries get hot during normal use, and they absorb a lot of heat from the engine. But if they get too hot, it may be a sign that they are having trouble storing power and coping with the engine’s heat.

A non-sealed battery can dry out over time, meaning there is less acid to store the energy. You should check the full-level on the battery to make sure it is not dry. Also, check that both contacts are good and have no corrosion, as this adds electrical resistance.

It is a good idea to get a multimeter. Once connected, the multimeter will give you an exact readout of the voltage left on the battery. Then making sure that there is nothing that can get in the way of the engine belts, you can start the engine.

As the engine runs, you will see the reading increase, but anything over 14.6 volts is a sign of overcharging.

What Happens if You Charge Your Car Battery for Too Long?

A standard car battery should take anywhere from six hours to four days to charge, depending on how careful you want to be. A standard car battery will hold up to 48 amp-hours, so a two-amp charger would take 24 hours from zero power.

You want to use a smart-charger or one with low amperage. When you fast-charge or overcharge the battery, the acid may heat to the point where it begins to evaporate.

If a lot of the water in the acid evaporates, there is nothing to cool the plastic casing or lead electrodes, and both will begin to warp. And if you keep going, you can crack the battery housing and destroy the unit.

Why Charge a Battery?

The safest way to restore a flat battery is by using a trickle charger. Jump-starting a car is fine in emergencies, but you will cause damage if you keep doing it. You may have a vehicle that you store over the winter months, and it is better to keep the charge up rather than letting the battery go flat.

Car batteries are tough and resilient to all sorts of weather conditions. Extreme cold will kill a battery, and having it on a light-charge through the winter will keep its core temperature above freezing.


Will the battery charge faster if I push the accelerator?

No! Revving your engine can damage a flat battery since you are giving it more energy than it can manage from flat. Let your engine idle and charge the battery at a lower voltage.

Is it OK to charge a battery overnight?

Intelligent trickle chargers work the best if you can leave them overnight. A good charger should have a trip fuse, which cuts the power to the battery if there is a problem. And a professional charger will control the power to give your battery the best charge.

What is the chance my battery will blow up?

Anything can happen. Car batteries have several fail-safe mechanisms to prevent overpressure. Car batteries still hold corrosive acid that needs treating with respect. It is rare for lead-acid batteries in a car with an engine to explode. Electric cars use more volatile electrodes that can explode.

How long does my battery take to charge after jumpstarting it?

You can leave your engine to idle for 20 minutes if you want it in the morning. Or you can slow-drive the vehicle around your neighborhood for 10 minutes to see how it feels before taking it further away.