Can You Charge A Car Battery While Still Connected?

by Phil Borges // in Car

It is indeed frustrating when you cannot get your car started, or it makes you stranded in the middle of nowhere.

This situation makes some people curious if is it ok to charge car battery while connected. A question that was asked by some and the answer can be found with some simple research.

This article will explore what you need to know about charging your car battery, including how long the process should take, what type of charger you should use, and more.

Can you charge car battery while connected?

Charging a car battery while still connected can be dangerous, but there are some steps you can take to reduce the risk of injury or damage to your vehicle.

It is always best to check the manual for your car to see what is recommended. Some of the best battery chargers on the market can charge your car's battery while it is still hooked up.

However, most car manufacturers will recommend that you turn the engine off before charging a battery. In this way, the alternator will supply enough power to both charge and run your car.

There are many variables and types for charging, not all of which can be used with any device or battery type without the risk of damage from overvoltage or short circuit dangers.

Charging time can vary between different chargers, and it is essential to follow instructions carefully so you do not damage your battery or charger in any way. Most quality batteries take at least four hours to charge.

When is the best time to disconnect the battery before charging?

1.If the battery is fully drained, it is best to disconnect it before charging. This will prevent the battery from leaking or causing damage to other parts of your car.

A trickle charger may be ineffective in charging a flat battery. This is because the low current flow of the trickle charge is not enough to overcome its internal resistance, and it gets even less effective as time goes on. You need something with higher currents that can recover batteries, but these chargers use pulsed currents that could cause damage if you put your car's battery under them during maintenance.

2.If you have an old version of a charger that is hard to find in the market nowadays. The older chargers are more likely to cause hazardous situations such as sparks or overcharging.

It is essential to have a modern charger for your car, or else you could damage its electronic systems. A microprocessor-controlled charger will limit the charging current and keep it at an appropriate level. In contrast, the older style chargers may provide too high of a current that can cause damages.

3.If you are using a lead-acid battery for charging. Car batteries used to be unsealed, which was a problem because they would vent hydrogen gas. This is highly explosive and could cause an explosion if it gets ignited in the engine compartment while charging them.

Ways to properly charge the car battery

If you do not know what to do, it is always best to check with your car manual or battery manufacturer to see what is recommended. Use a good quality charger for your vehicle, whether it is an older model or not.

If you have a modern microprocessor-controlled charger, it may be the best way to charge your car battery. This device will monitor the battery and charge it at the proper voltage.

Modern chargers will charge your battery at a rate of around 10% of the capacity. For example, if you have 100 amp-hour batteries, the charging current should not exceed 10 amps to avoid damaging them.

If your charger is old, it can be dangerous to leave it connected for too long. Older chargers cannot tell the difference between full and overcharged batteries, so they keep charging until you unplug them.

Here are some ways to charge the car battery:

1.Polarity check: Make sure that the battery terminals are in the correct orientation. The red cable must always go with positive, and the black one needs to be attached to the negative terminal of your battery.

A modern charger can tell when the cable is plugged in backward and stop charging your battery right away. Most older ones may not. In case of a reverse polarity connection, your charger could still damage diodes in your rectifier, so be very careful.

2.It is always best to connect the terminals in order, no matter how many steps are involved, then plug in the charger and switch it on.

3.The indicator will tell you when the charge is working.

4.It is always important to unplug the charger once you are done charging, or else sparks may ignite any gas that has escaped while it was being charged.


Would it be possible to start the car with the battery charger attached?

It is possible to start the car with the battery charger attached, but it is not advisable.

Chargers are not designed to provide a high current, say 100 amps max. When you try to start your car, the battery may be supplying only 10 amps of power. The charger will blow out and might even get damaged if it tries to draw in any more than that amount.

What can you get if you charge the battery while the engine is running?

If you leave the charger on while it is running, then it will keep trying to charge. It may also supply power for other components in your vehicle if they are not drawing enough on their own, like lights or dashboards.

What can happen if I do not take my battery out of my car?

It is possible that some of the chemical reactions within your car battery will cause it to become damaged.

If you do not take the battery out, there is a chance for leakage and the battery shorting out.


Getting a flat battery can be indeed annoying. It is frustrating to be without your car when you need it the most, and waiting for an hour or more while the charge finishes can seem like forever.

We hope that the guides above help you understand why it is crucial to take the battery out of your car when charging better than charging it while still connected for safety reasons.

About the author, Phil Borges

Phil Borges is a battery aficionado. He's written extensively about batteries, and he loves nothing more than discussing the latest innovations in the industry. He has a deep understanding of how batteries work, and he's always on the lookout for new ways to improve their performance.