A Guide to Charging a 12v Battery at Home

One of the most common battery types on the road today is the 12-volt battery. These batteries have been present since World War II and are used in trucks, cars, motorcycles, tractors, etc. They can either be placed standalone or in combination with other batteries to meet the specific on-demand requirements.

A 12-volt battery contains six 2-volt cells wired in series. The cells are made of lead-acid, and they store electrical energy and release it through a chemical process. There are a number of factors to consider when charging a 12V battery including Amperage, Voltage, and the size of the battery.

In this article we take you through the charging process, picking a charger, and how to charge a 12v battery.

What is the Charging Voltage for a 12v battery? 

When charging a 12v battery, the voltage should be between 13.2 and 14.4 volts. If the voltage is below 12.9 volts, the battery will not charge. Charging at a high voltage will give you faster charging and charging at a lower voltage will reduce the charging. 

If the voltage is above 14.4 volts, the battery will overcharge and this can cause gassing. 

Batteries when charged undergo a process called the charging cycle. This cycle includes four main stages: pre-conditioning, constant current charging, constant voltage charging, and float charging. 


Pre-conditioning is the first stage of the cycle and is used to prepare the battery for charging. During this stage, the battery’s voltage and temperature are checked.

Bulk Charging

In the second stage, a constant current is applied to charge the battery. This is also known as bulk charging, is when the battery is charged at a constant rate. This stage lasts until the battery comes to around 13v.


At this stage, the battery voltage is high which also raises the internal resistance of the battery. The third stage, constant voltage charging, is when the battery is charged at a constant voltage. 

The final stage, float charging, is when the battery is kept at a floating voltage to maintain its charge.

How much current (amps) is needed to charge a 12v battery 

The current or number of amps needed to charge any 12v battery depends on its capacity. Battery capacity is measured in Amp-hours (Ah)

For SLA batteries a current of not more than 10% of the battery capacity is recommended for charging. For example, a 100 Ah battery will require 10 amps to charge. This however can go twice depending on the battery type. A lithium battery can actually be charged with amps almost half its capacity for example a 50 amp-hour battery can take in more than 20 amps. 

This is dependent on the battery’s C rating. A battery’s C rating is a measure of how much current it can safely handle. A battery with a higher C-rating will have a higher capacity and be able to deliver more current than a battery with a lower C-rating. 

12-volt Deep cycle vs Starter Batteries 

Although both batteries are 12 volts there are several key differences between deep cycle and starter batteries. Starter batteries are designed to provide large boosts of power to start up engines while deep cycles are designed to be discharged for long periods. 

A deep cycle battery is not designed to handle rapid charging while a starter battery is not meant for regular use of deep discharge as they will die out quickly. 

How to Charge a 12v battery 

Batteries are charged by connecting them to a power source that provides the appropriate amount of voltage and current for the specific type of battery. The most common type of power source used to charge batteries is a wall outlet. 

Other power sources include car chargers, solar panels, and generators. The voltage and current required to charge a battery depend on the type of battery being charged. 

This is done by connecting the positive cable of the charger to the positive terminal of the battery, and the negative cable of the charger to the negative terminal of the battery. 

Black and Red Alligator Clips

The various connectors that you can use to attach the charger to the battery. The most common ones are alligator clips. You can also use O-ring terminals in fixed spaces. 

Some chargers made especially for car batteries allow you to charge the battery using the cigarette lighter plug in your vehicle.

How to Charge a 12v Battery with Power Supply 

Smart battery chargers are one of the most convenient ways to keep your 12v batteries charged. A smart battery charger is a device that charges batteries using a microprocessor to control the charging process. 

The charger monitors the battery voltage and current to optimize the charging process and protect the battery from overcharging. Smart chargers can also recondition batteries that have been damaged by overcharging or deep discharge.

The charger is capable of charging any 12v size battery. You can select a 3 amp charge rate for small-size batteries, a 10 amp charge rate for batteries 50 to 100 amp hours, and a 15 amp charge rate for batteries above 200 amp-hours. 

The maintenance cycle is automatic and safe, automatically turning itself on whenever a battery begins to drain or off when the full charge cycle has been completed.

Charging a 12-v Battery Off-grid 

There are various options to charge a battery in case you don’t have power from the grid. You can use another battery, a generator, or a solar panel. 

A solar panel gives the extra benefit as you only have to rely on sunlight which is freely and readily available every day. With the right size solar panel, you can charge a 12v battery of any capacity.  

Precautions when Charging a 12v battery 

Make sure to always connect the positive terminal first and then connect to the negative terminal. If you mix the two this can lead to issues. It is recommended to use a charger with reverse polarity protection that won’t allow charge through when you mix the two. 

Also, make sure to charge the battery in a well-ventilated area. Lead-acid batteries produce hydrogen gas when being charged which poses a risk to fires or explosions. 

Always use a charger (including solar panel chargers) with overcharge protection that will not overcharge and damage your battery. 

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