How Long To Charge 300Ah Battery? + Calculator & Charts

Wondering how long will it take to charge a 300ah battery? You’ve come to the right place, my friend.

In this post, I’ll explain the charging mechanism of solar batteries and how to calculate the battery charge time with solar panels or with a charger

Need an easy solution? Use my free battery charge time calculator to find out. “Enter the solar panel size, battery specs & charge controller type”

Solar panel charge time calculator

Solar Panel Size
Battery Capacity (Ah)
Battery Volts (V)
Battery Type
Battery Depth of Discharge (DoD)
Charge Controller Type

Note! Use this solar panel size calculator if you want to find out what size solar panel you need to charge your battery in desired peak sun hours.


keep reading, I’ll explain this in detail so next time you don’t need to use the calculator online and also some knowledge about the solar battery charging mechanism

Watch this video to understand the basics of batteries: Amp-hours, amps, watt-hours, c-rating, etc…

How Long To Charge 300Ah Battery? (Calculate in 6 steps)

  1. Convert battery capacity in watt-hours
  2. Multiply the battery capacity (Wh) by the battery depth of discharge
  3. Multiply the battery capacity after DoD by 1.15 for lead-acid, AGM, gel type batteries, and 1.02 for lithium (LiFePO4) battery
  4. Multiply the solar panel wattage by 0.8 to cover the solar panel efficiency rate
  5. Multiply the average solar panel output by 0.8 (if you’re using a PWM charge controller) or by 1.02 (if you’re using an MPPT charge controller)
  6. Now divide the battery capacity after the battery charging efficiency rate by the solar panel output after the charge controller

have any confusion? let’s calculate together!

1- 300ah battery in watts

12v 300ah battery is equal to 3600 watts.

To calculate the battery in watt-hours we use this formula

Battery in watt-hours = Battery capacity in Ah * Battery volts

2- battery capacity after Depth of discharge

Battery depth of discharge (DoD) is the percentage of the total capacity of a battery is been discharged

Every battery type has a different DoD limit

  • Lead-acid, AGM, and Gel: 50% DoD limit
  • Lithium (LiFePO4): 100% DoD limit

Let’s say you have a 12v 300ah lead-acid battery with a 50% Depth of discharge limit.

Battery capacity after DoD = 3600 * 50% = 1800 watt-hours

3- battery charging efficiency

There will be some power losses when charging battery cells which are known as the battery charging efficiency rate.

  • lead-acid, AGM, and gel batteries charging efficiency: 85%
  • lithium (LiFePO4) battery charging efficiency rate: 98%
Energy required to charge 300ah lead-acid battery: 1800 * 1.15 = 2070 watt-hours

Note! if you’re recharging your battery with a battery charger then divide this value by the output watts of the charge that you’re using.

4- Average solar panel output

in real-world conditions, you’d receive about 80% of the rate wattage output from your solar panel during peak sun hours

let’s suppose you have a 400-watt of solar panel kit.

average solar panel output: 400 * 0.8 = 320 watt-hours

That’s what I receive from my 400-watt solar panel on average per peak sun hour on a sunny day.

Not sure what are peak sun hours? click here to read this post in which I’ve explained it well.

5- Charge controller efficiency

The job of the charge controller is to regulate the voltage output from the solar panels in order to safely charge the battery.

But unfortunately, charge controllers aren’t 100% efficient. There are two types of charge controllers available in the market right now.

  • PWM charge controller efficiency: 80%
  • MPPT charge controller efficiency: 98%

let’s say you’re using an MPPT charge controller

Solar panel output after charge controller: 320 (average solar panel output) * 0.8 = 256 watts

6- final calculation

Now divide the energy required to charge the 12v 300ah battery by the solar panel output after the charge controller efficiency rate

2070 (from step 3) / 256 = 8 peak sun hours

A 12v 300ah lead-acid battery from 50% depth of discharge will take about 8 peak sun hours with 400-watt solar panels

How long to charge 300ah battery – chart

Here’s a chart on how long will it take to charge a 12v 300ah lead-acid & lithium battery with different size solar panels using an MPPT charge controller.

12v 300ah lead-acid battery

Solar Panel SizeHow long to charge 300ah battery?
100 watts26 peak sun hours
200 watts13 peak sun hours
300 watts9 peak sun hours
400 watts6.5 peak sun hours
500 watts5 peak sun hours
600 watts4.5 peak sun hours
700 watts3.7 peak sun hours
800 watts3.3 peak sun hours
900 watts3 peak sun hours
1000 watts2.6 peak sun hours
How long to charge 300ah lead-acid battery


  • 12v 300ah lead-acid battery from 50% Depth of discharge will take anywhere between 26 peak sun hours (with 100-watt solar panel) to 2.6 peak sun hours (with 1000-watt solar panel) to get fully charged

12v 300ah lithium (LiFePO4) battery

Solar Panel SizeHow long to charge 300ah battery?
100 watts46 peak sun hours
200 watts23 peak sun hours
300 watts15 peak sun hours
400 watts12 peak sun hours
500 watts9 peak sun hours
600 watts8 peak sun hours
700 watts6.5 peak sun hours
800 watts5.8 peak sun hours
900 watts5.2 peak sun hours
1000 watts4.6 peak sun hours
How long to charge 300ah lithium battery


  • 12v 300ah lithium battery from 100% Depth of discharge will take anywhere between 46 peak sun hours (with 100-watt solar panel) to 4.6 peak sun hours (with 1000-watt solar panel) to get fully charged

How fast can you charge your battery?

in order to maintain the battery life and health they are recommended be to discharged and charged at a specific percentage of current.

Here’s a list of every battery with their recommended max charging rate

  • lead-acid, AGM, and gel batteries: 25% of their capacity
  • Lithium (LiFePO4) batteries: 100% of their capacity

Note: Read the product description to get an accurate value

For 300ah battery the maximum charging current should be 75 amps or 900 watts @ 12v for 300ah lead-acid battery, and 300 amps or 3600 watts @ 12v for lithium battery

if you have a 24v battery then I’m assuming that you’d be using a 24v solar system (which is necessary), for this scenario multiply the max charging output by 24 and so on for a 48v system

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I'm an experienced Sales Consultant with a demonstrated history of working in the renewables and environment industry. Skilled in Photography, Customer Service, and Sales.

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