Calculate Battery Charging Time & Current: Step‑by‑Step Guide with 120Ah Example

How to Calculate the Charging Time and Charging Current for Battery Charging?

Easy Battery Charging Time and Battery Charging Current Formula for Batteries. (With Example of 120Ah Battery).

In the following simple tutorial, we will show how to determine the suitable battery charging current as well as How to calculate the required time of battery charging in hours with a solved example of 12V, 120 Ah lead acid battery.

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Below are the given formulas for required battery charging time in hours and needed charging current in amperes as follows.

Charging Time of Battery = Battery Ah ÷ Charging Current

T = Ah ÷ A

and

Required Charging Current for battery = Battery Ah x 10%

A = Ah x 10%

Where,

• T = Time in hrs.
• Ah = Ampere Hour rating of battery
• A = Current in Amperes

Example:

Calculate the suitable charging current in Amps and the needed charging time in hrs for a 12V, 120Ah battery.

Solution:

Battery Charging Current:

First of all, we will calculate charging current for 120 Ah battery. As we know that charging current should be 10% of the Ah rating of battery.

Therefore,

Charging current for 120Ah Battery = 120 Ah x (10 ÷ 100) = 12 Amperes.

But due to some losses, we may take 12-14 Amperes for batteries charging purpose instead of 12 Amps.

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Battery Charging Time:

Suppose we took 13 Amp for charging purpose,

then,

Charging time for 120Ah battery = 120 ÷ 13 = 9.23 Hrs.

But this was an ideal case…

Practically, it has been noted that 40% of losses occurs in case of battery charging.

Then 120 x (40 ÷ 100) = 48   ……   (120Ah x 40% of losses)

Therefore,  120 + 48 = 168 Ah ( 120 Ah + Losses)

Now Charging Time of battery = Ah ÷ Charging Current

Putting the values;

168 ÷ 13 = 12.92 or 13 hrs. ( in real case)

Therefore, a 120Ah battery would take 13 Hours to fully charge in case of the required 13A charging current.