How to calculate battery charging current and time?

150 Ah Solar Battery

Individuals who use batteries on large scale do care about battery charging current and time because batteries are delicate and need care. In this article, we’ll check out the way to calculate battery charging current and battery charging time. For the sake of an instance, we are taking a 12 Volts 150 Ah which we use at the inverters.

Charging an inverter battery like 150 Ah requires some hefty time, any newbie may make questions like:

  • How much current (Amps) is required to charge a 150 Ah battery?
  • How much time it will take to charge a 150 Ah battery?

Note: Here we are going to read some technical terms related to electronics so clear the basics first. Current is denoted in Amperage, Ampere, or Amps (A), and once we hold that current in the battery it becomes Amps hour (Ah).

Calculating battery charging current.

Here we should look for the C rating of the battery, the C rating defines at what percentage the battery can be charged and discharged of its total capacity which is rated in Ah (ampere-hour).

  • For a C5 battery, it should be 5% of the total Ah.
  • For a C10 battery, it should be 10% of the total Ah.
  • For a C20 battery, it should be 20% of the total Ah.

I have a 150 Ah battery that has a C10 rating on it, so the charging current should be 10% of its total Ah rating.

Ah (ampere-hour) is the rating used to tell consumers how much amperage a battery can provide for exactly one hour. This means you can drain a full 150 A in one hour, 50 A in 3 hours, and 15 A in 10 hours.

You can charge a battery using more current to decrease the charging time, but not all batteries are designed that way to handle more current. Charging a battery with more than needed current may damage it or shorten its life.

So here formula is very simple, just calculate the Ah’s C%.

I = Ah × C%

150 Ah × C10% = 150 Ah × C10/100 = 15 A (theoretical answer)

Practically you’ll need little more like +1 A or +2 A to charge a battery.

Calculating battery charging time.

Calculating battery charging time is easy too, all you need is Ah rating and current needs which you can calculate from the above sum. Here we’ll see how much it will take a 150 Ah battery to get charged fully.

So here formula will be a battery’s Ah rating divided by its charging current.

Time = Ah rating / I

150 Ah / 16 A = 9.375 Hours (theoretical answer)

Practically there are some charging losses due to which it could be more (13.125 hours) but close the above answer.

For a lead-acid battery, charging losses are 40%, so either adds an additional 40% value to Ah rating or to the final hours’ value. I have shown both the ways, just check them out carefully.

  • 150 Ah + (150 Ah × 40 / 100) / 16 A = 13.125 Hours.
  • 9.375 H + (9.375 H × 40 / 100) = 13.125 Hours.

Now using this simple technique you can calculate battery charging current and time of all sizes.

By Atul Kumar Pandey

Hi, I'm creator of atulhost, comes from business management and tech background. I love to do research on modern business insights and latest technological solutions.

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