Powering the car battery, how much time it takes?

Administrator posted this 24 September 2018

To find the answer to the question of the topic, you need to keep in the mind one rule, that there is no huge matter on the type of battery, as the matter of the way of charging the battery.

Important indicators for the battery:

1. The capacity (ampere per hour) means the amount of load, measurable in current intensity, which can be completely wasted during for one hour. For instance, if the battery capacity is 75A/h, and you give the same load at once, then after an hour the battery will run down. So, if the load value is lower, than the duration of work is higher.

2. The voltage is approximately 12.7 W, if the voltage is 11.7 W and less, it is dangerous and is considering as a deep discharge of the battery.

The first step for accumulator charging is to remove it out of your car. Before to do it, you need to clean battery terminals (use the water and soda bath). The next step is used to be only with the non-hermetic accumulator, or service battery. When preparing to charge this type of battery, it is important to check the electrolyte level, it should completely cover the plumbic plates. Otherwise, it is necessary to add distilled water to each bank separately, as the banks have no communication with each other. Boiling electrolyte is a signal that the battery is charged. As it was mentioned the service battery can be opened, so it is not recommended to charge it at home, in the case when you have pets or small children there.

Before proceeding, the answer to the main question, how long to charge the battery - will be variable, namely, this process can take from 4 to 12 hours.

It's quite simple, the voltage equal to 10% of the total capacity of the battery is optimal decision. Therefore, if you have a battery capacity of 100 A/h, the amperage is 10 A. in the case where the voltage-power was 11.5 W (the extreme value of the discharge), the battery capacity of 100A/h will be charged for 12 hours.

On average, the battery charge at 75 A/h at a rate of 11.7 W, will take 10 hours.

It is important to mention, that it is undesirable to bring the accumulator into a state of the full discharge. It is more useful to maintain the charge at rates of 50% (12 W), you can charge the battery 6-8 hours at a voltage-power of 1-2W, this is optimal to do at night.

There were conditions of the charging at a constant current, above, but more common is the constant-voltage charging, which is adapted for the hermetic accumulator.

The voltage conventionally is in the range of 13.8 — 14.5 Watts. At this voltage, the battery absorbs 60% of the charge for the first hour, then 20%, for the third hour consumption is 8% and by the fourth hour the charge capacity reaches 90%. (in the conditions of the deep discharge). But the full charge, with this method, needs time. The current drops to decimal values, and 100% is achieved in 5-6 hours.

In such case, 100% of the accumulator charge, in conditions of constant-voltage powering, takes about 10 hours, as well. But you can charge the battery to 90% of power in 4 hours, because of the measured strength of the charge voltage.

While at a constant current, the charge takes 6-8 hours if the discharge level is about 50% or 10-12 hours at a deep discharge.

The voltage and the capacity



The charging at a constant current

The constant-voltage charging

12,7 W




11,5 W (for 100 A/h)


12 hours

12 hours

11,7 W (for 75 A/h)


10 hours

12 W


6-8 hours

4-5 hours (to 90%)

6-8 hours (to 100%)

*values - are given for batteries with a capacity of 100 and 75 A/h, and the difference for batteries of lower capacity will be less by 1-1.5 hours of charge from the indicators in the table.