Guide About Charging a Car Battery Overnight

Guide About Charging a Car Battery Overnight

Can You Charge a Car Battery Overnight?

Ever left your headlights on all night and the car would not start in the morning? A dead car battery is a common problem that can happen due to various reasons. In such a case recharging your car batteries is necessary but a lot of people go for an over-night charge. That is not only bad for the battery but it can also lead to hazardous results like an explosion or short circuit. Charging your car batteries using a manual charger all night can cause short circuits and fire. A 10 amp charger can cause damage to your car battery as it does not drop down the current to 2-3 amp after a full recharge. After you connect the battery to your car, alternator also continues to recharge the battery and within a few days symptoms of over-charging occur at the positive terminal of the battery.

Using an intelligent charger like the new ones in the market is a better option as they shut down once the battery reaches its maximum charging capacity even you can leave them for a few weeks. These chargers drop their current to almost ½ amp which makes it quite safe to leave the charger on for a couple of days. Despite having smart chargers, it is highly recommended to NOT charge the car batteries overnight. Take an overnight trip instead, this will charge it right up for you without causing any damage or putting your battery at risk.

How to Charge a Car Battery with a Wall Outlet?

How to Charge a Car Battery with a Wall Outlet

Charging a car battery with a wall outlet is quite easy. All you need are a couple of things and the right method and voila!
Here is what you will be needing:

  • Battery charger
  • Wrench
  • Electric safety gloves


  • Clean the working area. Make sure there is no moisture around the charger, battery, or on the gloves.
  • Open the hood of the car and loosen up each of the terminals of the battery using a wrench.
  • Once loosened up, remove the negative terminal (first) and then the positive terminal.
  • Once you have disconnected everything, take the black wire of the charger and connect it to the negative terminal and the red wire to the positive one.
  • Once a reliable connection has been established, then set the charging current. Make sure that the charging current should be according to the battery capacity. I would recommend not taking the current above 10% of your battery’s capacity for better life of the battery.
  • Now that everything is correctly done, plug in the charger switch in the wall outlet and begin the charging.
  • The charging time majorly depends on the battery’s capacity. The higher the capacity the higher the charging time.

How to Charge a Car Battery with Another Car?

How to Charge a Car Battery with Another Car

Charging car batteries with another car is known as the jump-start method. This method is very useful especially when you are in a remote area where a mechanic or charging outlets are hard to find. In this method, a dead car battery is charged with the battery of another car.
Steps of the jump-start method are:


  • Park the car with a good battery close to the one with a dead battery. The distance should be around 18 inches. It will give you sufficient room to work between them. Do not let them touch.
  • Next, you have to prep them for the jump start by putting the vehicles in neutral (or park for an automatic car). Also, turn off all electrical components of both cars. The ignition should be off for both cars.
  • Then, locate the negative and positive terminal on the batteries and the jumper cables. They are usually color-coded (red is positive and black is negative).
  • Begin with the dead battery and attach the positive clamp to the positive terminal of that battery.
  • Take the same jumper cable and attach the other positive clamp with the terminal of the good battery.
  • Then attach the negative clamp of the jumper cable to the negative terminal of the good battery, and the other end to an unpainted metallic area (away from the moving parts).
  • Now its time to charge up. Start the car with a good battery and wait for a couple of minutes. If you are in a cold region, you will have to wait a little longer. In this way, you are sending electricity to the bad battery.
  • After you charge the bad battery for a while, Switch on the ignition of the car with a bad battery and try to start. If it works remove the jumper cables in reverse order as you put on.
  • When the car start let it run for 15-20 mins and it will be good for a ride.

Looking for Jumper Cable? TOPDC 4 Guage 20 feet long Jumper Cables is the best choice to buy with a carry bag. You should keep this pair of cables in your car if you have issues with your car battery.

I often get asked about How long to recharge the car battery after the jump? It usually takes around 30 min at a minimum. If your vehicle still does not start after charging for 30min you might want to recheck the connection or recharge for more time. If still, the car won’t start, there might be a bigger problem than just a dead battery.

How Long to Charge a Car Battery at 6 Amperes?

The time that a battery takes to become fully charged depends entirely on the capacity of the battery. For a battery of 50 Ah (completely discharged), 8.3 hours are required to completely charge it. However, for a 100 Ah battery, around 16 hours are consumed for fully charging it.

Let’s find out How to Determine the charging time?

Here is a formula for calculating the charging time:
The time it takes to charge a battery = (battery capacity x depth of discharge) / amperage of the charger

  • Battery capacity: It is measured by Ah (ampere-hours) and is mentioned on the body of the battery.
  • Depth of discharge: It is the amount of discharge that has been removed from a fully charged battery. The value is taken in percentage. Normally it is taken as fully discharged which is 100%.
  • The amperage of the charger: The charging current of the charger. It is between 2-30Ah.

Let’s take an example, the time take to charge a battery of 50 Ah at 6 ampere charging current is:
T = 50 x 100% / 6
T = 50/6
T = 8.3 Hours

How to Charge Car Battery at Home with Laptop Charger?

Using a laptop charger to charge your car battery sounds like a weird plan but believe me it works perfectly. Here is what you will be needing to get this job done:

  • Wires
  • Wire stripper
  • Voltmeter
  • 12 Volt bulb
  • Laptop charger


  • To use the laptop charger, you need to first determine the positive and negative wire. To do this, use a wire stripper and cut the pin. With the help of a voltmeter determine the positive and negative wire. Normally, black wire represents negative.
  • As laptop charger voltage is about 19 Volt, create a series connection of the 12-volt bulb, charger, and the battery to maintain the voltage level.
  • Do not forget to open the electrolyte inlets of the battery during this process as charging creates gasses and emission which must leave the battery.
  • Once the connection has established, switch on the charger and start charging, until you see bubbles in the electrolyte. Bubbles is the indication of the battery being charged. That is when you need to unplug things and disconnect the wires. You can also check the voltage of the battery with a voltmeter before and after the charging to make sure of that.

Can You Leave a Car Battery Charger ON for too long?

Charging time depends on the battery’s capacity but it is not safe to leave the battery charging for a long time. The answer entirely depends on the type of charger you use. A smart automatic charger like NOCO Genius 10Amp Charger compensates for the human error; even if you forget and leave it on for quite a long it will automatically stop charging. However, if you are charging with a manual charge and have left it on for quite a long, it can be very hazardous.

If you are using a manual charger, unplug immediately once the charging is completed or reduce the charge to the minimum amperes to avoid any damage.

Can I Trickle Charge a Battery Without Disconnecting it?

Some electronic components of the car like alarm system work even when the ignition is switched off. Yes, You can trickle charge a battery without disconnecting it, but you have to make sure that all such electronic components are disconnected otherwise they can be damaged.

Connect the red or positive wire of the charger with the positive terminal of the battery. For black or negative wire, locate a suitable ground location. Ideally, I would use the bare metal frame or a large bolt from the chassis or engine block. However, if you cannot locate one, use a clean section of the metal frame; it will work just as good. Just make sure there is no dirt, moisture or oil on there. After connection set the amperage and charge your battery.

Note: Never use the negative terminal of the battery for charging without disconnecting, as it can lead to an explosion or can cause a fire.

What can Drain a Car Battery Overnight?

There are various reasons behind overnight battery drainage. You can avoid the following to ensure this does not happen to you.

  • Corroded or Loose Battery Terminals

If the battery terminals have gone through corrosion, have heavy deposits on, or are not properly tight, it can lead to the poor charging of the battery. Battery will not properly charge hence drain quickly.

  • Poor Battery Condition

If the battery of your vehicle is worn out or very old, there is a chance it will lose charge very quickly.

  • Leaving lights on

Leaving the lights on (ignition switch) can drain out battery very fast.

  • Faulty Alternator Diode

A defected alternator diode is one of the most common reasons for overnight battery drainage. If you find even the slightest problem in it, it is best to replace it immediately to avoid battery problems.