How to Charge a Car Battery at Home 120w portable solar panels for camping

Car batteries have a limited use-by date. They are often neglected and are subject to heat and vibration from your vehicle. Over time they will naturally lose their ability to hold a charge.

If you don’t use your vehicle for a long time you may find that your battery will self-discharge. This is normal and will be more evident if you have alarm systems and keyless entry on your car.

In this post, we are going to cover how to charge a car battery at home with and without a charger the right way. Hopefully without damage to yourself, the vehicle, or the battery.

Always use eye protection when working on car batteries and be careful not to cause a short circuit.

How to charge a car battery without a charger?

How to Charge a Car Battery at Home 120w portable solar panels for camping

There are many ways to charge a car battery without a charger. It is best to remove the battery from the car if you are using a DIY 12v battery charger solution.

  • Use another fully charged car battery connected with jump leads. Leave them connected together for 1/2 hour.
  • Start your car and drive around for 1 hour to charge it up.
  • Use a portable solar panel 12v battery charger.
  • Install your battery into another car to charge it up.
  • Use a wall power supply that has an output between 12v and 18v DC.
  • Use a portable jump starter to charge the battery.
  • Take it to a battery retailer and ask for a capacity test. They will charge it up for you and give you a test report.

Even though the above methods work in emergencies I would recommend using a quality 12v smart battery charger for motorcycles and cars.

Always connect the red positive lead of the charger to the positive ( + ) connection point on the battery. The black negative of the charger to the negative ( – ) of the battery.

Charging a car battery overnight

how to charge a car battery without a charger?

There is no problem charging a car battery overnight. In fact, it is recommended to do a top-up charge every few months to prolong the battery life.

If your battery is fully discharged or flat you will need 12 hours or more to charge it up fully.

Just be sure to check the battery water level before and after you have charged it. Some newer car batteries are maintenance-free and so you are unable to open them up to check.

Can I trickle charge a battery without disconnecting it?

Can I trickle charge a battery without disconnecting it?

Yes, you can trickly charge a car or boat battery without disconnecting it from the vehicle. Just be sure to keep checking the battery acid level. It is also a good idea to keep the hood open as you charge it up for ventilation.

I use a Ctek smart charger on my car, motorcycle, and Seadoo jetski. If they are going to sit unused for a few months. I connect up the trickle charger for a few days and then remove it once the battery voltage has stabilized.

If you would like more information we have done a post on the safety of charging a car battery while still connected to your vehicle.

Can you charge a car battery in the house?

I would not recommend charging a car battery in the house. When the 12v car battery is charging it generates hydrogen sulfide gas that is explosive in certain concentrations in air. The gas is colorless, very poisonous, and has the odor of rotten eggs.

It is best to charge the battery outside in a well-ventilated area. If you do have to charge a car battery in a room make sure that there is an extraction fan always running.

It is much safer to leave the battery in the car. It is how I charge a car battery at home.

How long to charge a car battery?

Charging a Car Battery While Still Connected to your Vehicle toyota
Toyota Highlander battery being charged with a Ctek smart charger.

You should be able to fully charge a car battery overnight with a 5-amp 12v charger. These will top up your battery to the correct level and then float at the correct voltage with a trickle top-up.

For example, if your car battery is a 60Ah battery and you charge it from under 12v to full it will take around 12 hours using a 5A charger.

If you use a 1Ah battery charger it will take around 60 hours to charge the same battery.

5Ah x 12hours = 60Ah capacity.

This is why you should go for a car battery charger that is at least 5Ah or faster charge. Some chargers let you set the charge rate for different size batteries. My Ctek car battery charger can be selected between 1-5 amps with just a press of a button.

Eg: A motorcycle battery can be charged on 1Ah and will only take a few hours due to the battery being smaller in size.

Car battery voltage chart

ChargeSealed or Lead Acid 
battery voltage
Gel battery
100%12.70+ Volts12.85+ Volts
75%12.40 V12.65 V
50%12.20 V12.35 V
25%12.00 V12.00 V
0%<11.8 V
Battery Sulphate risk
<11.8 V
Battery Sulphate risk

Any voltages under 12v and your car will most probably not crank over. There is not enough reserve power to turn over the starter motor.

There will still be power for the radio and lights but not for starting the car. This is why some people think that their battery is ok because they have lights working on their car.

If you hear a ticking sound or if your car is cranking over slowly then your battery is flat or under 11.8V.

Is your car battery charging slowly?

There are three reasons that your car battery is charging slowly at home.

  1. Your charger is set to charge at 1 amp or less.
  2. Your car battery is faulty and unable to hold or store a charge.
  3. The fluid level in the battery is low.

Check the correct battery acid/water level and top up if required. If there is any bulging of the battery case you could have damaged cells and you need to replace the battery.

sulfation of car battery cells
Checking car battery water level and build up of sulfer on the lead cells.

Sometimes if the car battery has been left under 12v for a long period of time you can get Sulphation on the lead plates. You can try using a smart charger to desulphate the car battery.

Sulfation is a buildup of lead sulfate crystals on the cell walls of the battery. These crystals over-time will grow and cause a short circuit in the battery. Keeping your battery above 12v or fully charged will slow down the crystal growth so your battery lasts longer.


Often our car batteries go flat at the worst possible times. Be sure to keep a jump starter and a battery charger handy at home. Always charge your car battery at home in a well-ventilated area.

If you have a quality jump starter and a 12v smart charger you will never have issues again with not being able to start your car. But if not being able to charge your car battery without a charger using the above tips and tricks may get you out of a sticky situation in an emergency.

Over time batteries do fail. They become old and have sulfate build-up on the lead cell plates. I like to replace my car, motorcycle, and boat batteries every 4 years. This is a small cost to make sure I have the correct capacity and high cold-cranking amps when I need them.

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