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Charging requires not only a completely dead battery (it is not advisable to bring this up), but also a battery in use. But **recharge time** will be with them **different**. Often this **from 8 to 12 hours**. Our online calculator will help **calculate how much you need to charge a car battery**, using direct current for this.

## When, how and with what current to charge

As a rule, the degree of battery charge is judged by the density of its electrolyte. The density of a fully charged battery should be 1.26-1.28 g / cm³, the voltage should be at least 12.5 V. Everything will depend on what electrolyte density was originally set in the new battery in your region of residence, it may be 12.7 So 12.9V. The lower the density, the more it is discharged. A decrease in density by 0.01 g / cm3 compared to the nominal value means that the battery is discharged by about 6-8%. The degree of charge should be determined by the bank with the lowest density.

A lead-acid battery, which is discharged by more than 50% in the summer and even more than 25% in the winter, must be removed and recharged. Also, an additional battery requires that battery whose density in the banks differs by more than 0.02 g / cm³.

The optimal battery charging current is considered **current equal to 0.05** from its capacity (**surge charge**) So for a battery with a capacity of 55 Amp / h, this value is 2.75 A, and for 60 Ah it is already 3 amperes. The purpose of this method is to ensure complete restoration of active masses in all plates of the battery.

Although often used the so-called **forced charge** and take a different ratio. **10% of capacity**. That is, a standard car battery **55Ah charge 2.75-5.5A**, and for **60Ah battery** charging current is set within **from 3A to 6A**. But, you need to know that the smaller the charging current, the deeper the charge, although it takes more time. Exactly the same situation with the feed **voltage. the more the faster**, but it **should not fall below 13.8** and **exceed 14.5V**) Charging voltage up **up to 16.0-16.5V** only **when charging a maintenance free battery**.

## Video: How Much Charge a Screwdriver Battery

Be sure to note that today there are several methods for recharging the battery:

- At a direct current;
- With constant voltage;
- Combining in automatic mode (we will not consider, because in this case a time calculator is not needed).

Car Battery Low Stages

## Battery Charging Time at DC

The formula for calculating the charging current is: I = Q k, where Q is the battery capacity, and k is a certain coefficient of the nominal value (its ideal value is in the range 0.04. 0.06, and the optimal one is up to 0.1). Based on this recommendation, the calculation of the time it takes for a fully-charged battery has the following form: T = Q / I. Substituting your values, you will see that it turns out quite a lot of time, but since often it’s not necessary to fully charge, but only to restore the capacity, then this figure will be two or one and a half times less.

For a rough estimate of the required time to charge the car battery **direct current** First you need to determine the degree of battery drain (in percent), then determine the lost capacity (in Ah), and then, choosing the amount of charging current, calculate the time of full charge. The formula for calculating how long it takes to recharge a car’s battery looks like this:

Multiplying this ratio by 2 times is necessary due to the fact that the process efficiency is 40-50%, the rest is spent on heating, as well as the related electrochemical processes.

When for an hour at the battery terminals, when charging, the voltage stops increasing. the battery is 100% charged.

The magnitude of the final voltage depends on: the magnitude of the charging current, temperature, internal resistance of the battery, the presence of impurities in the electrolyte and the composition of the alloy lattices.

## How to use a calculator

To find out how long it takes to charge your battery, you do not need to go into the details of all processes and calculation formulas, just use this calculator.

For online calculation, you need to fill in all three fields:

- In the field "Nominal capacity" enter the capacity of the rechargeable battery.
- In the “Degree of discharge” field, you can enter both the percentage ratio calculated according to the table, and the voltage measured with a voltmeter.
- In the “Charging current” cell, you need to indicate which current you plan to charge the battery from the charger.

By pressing the button “Calculate” you will receive the necessary time for a full charge of the car battery.