Charging the car battery overnight. What you should know

A common misconception is that leaving the battery charging overnight will cause damage to either the battery or other vehicle components. This is not true when charging at low amperage as one would do with a trickle charger when engaging in maintenance/storage charging and using more than 12 volts will usually result in overcharging (due to voltage drop) which can lead to gassing (the electrolyte boiling out of solution) and acid corrosion of both lead plates inside the cells).

It is safe to leave my car battery charging overnight?

Yes, it is safe to leave the battery charging overnight but the time can also increase (defined as 48 hours or more) assuming you have maintained the battery properly and provided a full charge periodically. The benefits of keeping your car battery charged are many.

A fully charged battery provides smoother, quicker acceleration, increased battery service life, and fewer alternator switches clicking on and off due to low voltage.

If you are going to leave your car battery to charge overnight, make it a point not to drive the car for at least 24 hours before leaving it for charging because this will reduce “stress” on the vehicle and allow the battery enough time for a good charge.

What are the risks of charging the car battery for too long?

It is never advisable to overcharge a car battery. When the voltage of the battery reaches 15.9 volts, this state of charge may be considered as permanently damaged (or sulfated). Plugging in an electric car charger can put extra stress on your car battery and cause it to die prematurely.

This is because charging will heat up the cells and acid inside them. Some overcharged batteries can even explode due to heat build-up inside it, or even due to pressure from gases created within them.

Another disadvantage of leaving the car battery charging for too long is when the charging system does not shut off when the batteries are charged. This will result in overcharging which can be dangerous and can ruin the battery, so be careful when you buy a charger, better pay more for a quality one.

Battery chargers that do not have a timer or on/off switch for the charge will have to be unplugged manually to prevent overcharging. It is always advisable to be cautious and not to leave the battery charger plugged in after the battery was charged.

The life of a lead acid battery is reduced when you fail to fully and correctly charge it after each use, resulting in loss of electrolytes (sulfation).

What kind of charger does my car battery need?

Choose a charger that is suitable for your battery. Most chargers are universal and will work for all types of batteries, except for gel batteries. There are quick chargers out there that can charge your battery quickly and will even give you a quick start.

There are also chargers that charge slowly but better. Many modern devices have a microprocessor that allows you to control the charging state of the battery. This is very convenient because the charging process stops automatically after the battery is fully charged.

Simpler and older models, as I have mentioned above, need to be stopped manually to prevent dangerous overcharging. You should be very careful and not let it connected for a long time. Read the instruction manual of your charger to make sure you are using it correctly.

Even modern digital models must be carefully monitored during charging to ensure that they function properly and stops charging is complete.

These above car battery chargers are all tested and gave me good results.

Sale
NOCO GENIUS1, 1-Amp Fully-Automatic Smart Charger, 6V and 12V Battery Charger, Battery Maintainer, Trickle Charger, and Battery Desulfator with Temperature Compensation
20,931 Reviews
NOCO GENIUS1, 1-Amp Fully-Automatic Smart Charger, 6V and 12V Battery Charger, Battery Maintainer, Trickle Charger, and Battery Desulfator with Temperature Compensation
  • Meet the GENIUS1 - Similar to our G750, just better. It's 35% smaller and delivers 35% more power. It's the all-in-one solution - battery charger, battery maintainer, trickle charger, plus battery desulfator.
  • Do more with Genius - Designed for 6-volt and 12-volt lead-acid automotive, marine, and deep-cycle batteries, including flooded, gel, AGM, and maintenance-free, plus lithium-ion batteries.
  • Enjoy precision charging - An integrated thermal sensor detects the ambient temperature and alters the charge to eliminate over-charging in hot climates and under-charging in cold climates.
  • Charge dead batteries - Charges batteries as low as 1-volt. Or use the all-new force mode that allows you to take control and manually begin charging dead batteries down to zero volts.
  • Restore your battery - Automatically detects battery sulfation and acid stratification to restore lost battery performance for stronger engine starts and extended battery life.
Sale
NOCO GENIUS5, 5-Amp Fully-Automatic Smart Charger, 6V and 12V Battery Charger, Battery Maintainer, Trickle Charger, and Battery Desulfator with Temperature Compensation
8,087 Reviews
NOCO GENIUS5, 5-Amp Fully-Automatic Smart Charger, 6V and 12V Battery Charger, Battery Maintainer, Trickle Charger, and Battery Desulfator with Temperature Compensation
  • Meet the GENIUS5 - Similar to our G3500, just better. It's 34% smaller and delivers 65% more power. It's the all-in-one solution - battery charger, battery maintainer, trickle charger, plus battery desulfator.
  • Do more with Genius - Designed for 6-volt and 12-volt lead-acid automotive, marine, and deep-cycle batteries, including flooded, gel, AGM, and maintenance-free, plus lithium-ion batteries.
  • Enjoy precision charging - An integrated thermal sensor detects the ambient temperature and alters the charge to eliminate over-charging in hot climates and under-charging in cold climates.
  • Charge dead batteries - Charges batteries as low as 1-volt. Or use the all-new force mode that allows you to take control and manually begin charging dead batteries down to zero volts.
  • Restore your battery - Automatically detects battery sulfation and acid stratification to restore lost battery performance for stronger engine starts and extended battery life.
Sale
NOCO GENIUS5, 5-Amp Fully-Automatic Smart Charger, 6V and 12V Battery Charger, Battery Maintainer, Trickle Charger, and Battery Desulfator with Temperature Compensation
8,087 Reviews
NOCO GENIUS5, 5-Amp Fully-Automatic Smart Charger, 6V and 12V Battery Charger, Battery Maintainer, Trickle Charger, and Battery Desulfator with Temperature Compensation
  • Meet the GENIUS5 - Similar to our G3500, just better. It's 34% smaller and delivers 65% more power. It's the all-in-one solution - battery charger, battery maintainer, trickle charger, plus battery desulfator.
  • Do more with Genius - Designed for 6-volt and 12-volt lead-acid automotive, marine, and deep-cycle batteries, including flooded, gel, AGM, and maintenance-free, plus lithium-ion batteries.
  • Enjoy precision charging - An integrated thermal sensor detects the ambient temperature and alters the charge to eliminate over-charging in hot climates and under-charging in cold climates.
  • Charge dead batteries - Charges batteries as low as 1-volt. Or use the all-new force mode that allows you to take control and manually begin charging dead batteries down to zero volts.
  • Restore your battery - Automatically detects battery sulfation and acid stratification to restore lost battery performance for stronger engine starts and extended battery life.

Digital chargers can indicate the voltage level in the battery and allow you to set the desired voltage level. Older models will only allow you to turn on and off the charging process. Speed ​​chargers also allow you to choose the speed at which you want to charge the battery.

Fast charging is good for a car battery that has recently run out because of a mistake like leaving the headlights or radio on. If the battery has been discharged for a long time, it may take a longer charging process before it can be used. If the device allows you to set the desired battery voltage, then put the value indicated on the label.

Never put the charger in fast charging mode if you plan to leave it overnight. If the slow charging mode is selected, the battery can be left there. There are two charging modes: constant current or constant voltage. The first method is more effective because it does not require control.

The second method is simpler, but it allows you to charge the battery only up to 80%. Some expensive charging models offer a combination method that minimizes human intervention. 

Scroll to Top