How Long To Charge 120ah Battery? (+ Calculator)

12v 120ah lead-acid battery from 50% Depth of discharge will take anywhere between 10.5 peak sun hours (using 100 watt solar panel) to 2 peak sun hours (using 500 watt solar panel) to get fully charged.

There are many things to consider when measuring “How long to charge a 120ah battery?.”

To make this easy for you, I have made a battery charge time calculator. “Enter the battery specs, its depth of discharge, and the solar panel wattage” to find out how many hours you’d need to charge the battery.

Also, I’ll explain how long the 120ah battery will take to recharge with a charger. Keep reading…

Solar panel charge time calculator

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

Note: Click here to find out what size solar panel you need to charge your 120ah battery in desired hours.

About calculator

The battery charging time will be mentioned in peak sun hours. You may ask, “What are peak sun hours?” Click here to read the post in which I’ve explained it in detail. But in short,

  • 1 peak sun hour = When the sunlight intensity reaches an average of 1000 watts per meter square (1kw/m2).
  • Use this calculator to find out how many hours of peak sunlight your location receives per day.

What is Battery Depth of Discharge or DoD? It’s the percentage of the battery that has been discharged from its total capacity.

Example: how long to charge 120ah aGM battery

Let’s suppose you have a 12v 120ah AGM battery with a 50% depth of discharge. A 200 watt solar panel system using an MPPT charge controller.

how long to charge 120ah battery
Screenshot from the calculator: Enter the solar panel wattage, battery capacity (120) its voltage (e.g 12 for 12v), select the battery type, Enter its depth of discharge (e.g 50 for 50% depth of discharge) and select the charge controller type, Then click “CALCULATE” to find out how long to charge 120ah battery with solar panel

12v 120ah AGM battery will take about 5.2 peak sun hours to get fully charged from 50% depth of discharge with 200 watt solar panel using an MPPT charge controller.

Now let’s dive deep into manual calculations about how long to charge the battery with a solar panel or with a charger.

Some factors which will affect the battery charge time:

  • Lead-acid and lithium battery charging efficiency.
  • How fast can you recharge your 120ah battery?

120ah battery charge time with solar panels (Calculation)

First of all, let’s discuss how much solar power is needed to charge a 120ah lead-acid or lithium battery.

And then we’ll discuss how much power output you can expect from the solar panels.

⚠️ Spoiler Alter! solar panels will produce only 80% of their rated wattage capacity during peak sun hours.

How much solar power is needed to charge 120Ah battery?

First, let’s convert the 120ah battery capacity from amp-hours (Ah) to watt-hours (Wh) or watts.

Formula: Battery capacity in watts = Battery Ah * Battery Volts.

Let’s suppose you have a 12v 120ah battery.

120ah battery how many watts? 1440 watts (120 *12)

As you might know, Every battery type has a different “Depth Of Discharge Limit (DoD)”.

  • Lead-acid, AGM, and Gel: 50% depth of discharge limit, which means you can only use the half capacity of your battery. In this case 60Ah or 720 watts @ 12v.
  • Lithium-ion (LiFePO4): 100% depth of discharge limit, which means you can fully discharge your battery without damaging it.

Note: Check the battery specs sheet or ask your manufacturer to get the accurate DoD limit of your battery.

Multiply the battery capacity (Wh) by 0.5 for lead-acid, AGM, and Gel.

1440 * 0.5 = 720 watts.

Now let’s discuss the “Charging Efficiency” of different battery types.

  • Lead-acid, AGM, and Gel: 85% charging efficiency rate on average, means there’ll be an average of 15% of power loss when charging this type of battery.
  • Lithium-ion (LiFePO4): 98% charging efficiency rate, means there’ll be only 2% power loss when charging a lithium (LiFePO4) battery.

Let’s say you have a lead-acid battery, To cover up the losses multiply the battery capacity (Wh) by 1.15 for lead-acid or by 1.02 for lithium type battery.

720 watts * 1.15 = 828wh.

1470 watts of solar power for 12v 120ah lithium (LiFePO4) battery or 828 watts of solar power for a 12v 120ah lead-acid battery would be needed to recharge the battery.

average solar panel output in real world?

Now let’s discuss how much power output you can “ACTUALLY” expect from your solar panels in real-world conditions.

On average, a solar panel will produce about 80% of its rated wattage output in real-world conditions during peak sun hours.

This means on average, a 200 watt solar panel will produce about 160 watts of power output per peak sun hour.

This is what exactly i receive from my Renogy 200-watt solar panels.

Full Article: What Will A 200-Watt Solar Panel Run? (Sharing My Experience).

Let’s say you have a 200 watt solar panel and your location receives about 5 peak sun hours (PSH) per day.

200 * 0.8 =  160 watts of output per peak sun hour from 200 watt solar panel
160 * 5 = 800 watts of output per day  from 200 watt solar panel

Charge controller efficiency

The charge controller regulates the power produced by the solar panels to safely charge the battery.

There are two most commonly used solar panels PWM & MPPT.

  • PWM charge controllers are about 80% efficient.
  • MPPT charge controllers are about 98% efficient.

To take these power losses into account, Multiply the solar panel’s average wattage (per peak sun hour) by 0.8 if you’re using a PWM charge controller or by 0.98 if you’re using an MPPT charge controller.

160 * 0.8 = 128 watts

Calculation

Formula: Solar power required to charge the battery / Solar panel output after charge controller (per peak sun hour).

I’ll carry on with the previous calculations that we’ve made. Which are…

  • 828 watts of solar power is required for a 120ah lead-acid battery.
  • 200-watt solar panel, and a PWM charge controller.
828 / 128 = 6.4 peak sun hours

How long to charge 120ah battery with charger?

To calculate how long it takes to charge a 12v 120ah battery with a battery charger, “Divide the battery capacity (Ah) after its DoD and charging efficiency by the charger amps (A)”.

For example, 120ah lead-acid battery with a 50% DoD limit, and a 5A charger.

120ah * 50% DoD = 60Ah. 
60ah * 1.15 Charging efficiency = 69Ah. 
69ah / 5A (Charger) = 13.8 hours.

Here’s a list of how long to charge a 120ah lead-acid battery with a different amp charger.

  • How long to charge 120ah battery with 2 Amp charger? 34.5 hours.
  • How long to charge 120ah battery with 4 Amp charger? 17.2 hours.
  • How long to charge 120ah battery with 10 Amp charger? 6.9 hours.
  • How long to charge 120ah battery with 20 Amp charger? 3.4 hours.
  • How long to charge 120ah battery with 40 Amp charger? 1.7 hours.

Maximum Charging Current For 120ah Battery?

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

Here’s a list of different types of 120ah batteries with their maximum charging current.

  • 120ah lead-acid, AGM, and gel batteries: 30A or 360 watts for 12v battery or 720 watts for 24v battery.
  • 120ah Lithium (LiFePO4) battery: 120A or 1440 watts for 12v battery or 2880 watts for 24v battery.

Note: Read the product description to get an accurate value.

Full Article: Maximum Charging Current & Voltage For 12v Battery.

How long does it take to charge 12V 120Ah battery? – Chart

Here are charts on how long to charge 12v lead-acid and lithium batteries with solar panels using an MPPT charge controller.

How long To Charge 120ah Lead-acid Battery?

Here’s a chart on how long to charge a 12v 120ah lead-acid battery from 50% depth of discharge with different size solar panels using an MPPT charge controller.

Solar Panel SizeHow long To Charge 12v 120ah Lead-acid Battery?
100 watts10.5 peak sun hours
200 watts5.2 peak sun hours
300 watts3.5 peak sun hours
400 watts2.6 peak sun hours
500 watts2 peak sun hours
Table: How long to charge a 12v 200ah battery

Summary

  • How long will a 100W solar panel take to charge a 120Ah battery? A 100 watt solar panel will take about 10.5 peak sun hours to fully charge a 12v 120ah lead-acid battery from 50% depth of discharge.

how long to charge 120ah lithium battery?

Here’s a chart on how long to charge a 12v 120ah lithium (LiFePO4) battery from 100% depth of discharge with different size solar panels using an MPPT charge controller.

Solar Panel SizeHow long To Charge 120ah Lithium Battery?
100 watts19 peak sun hours
200 watts9 peak sun hours
300 watts6 peak sun hours
400 watts4.6 peak sun hours
500 watts3.7 peak sun hours
Table: How long to charge a 12v 200ah lithium battery

Summary

  • 12v 120ah lithium (LiFePO4) battery will take anywhere between 19 peak sun hours (using 100 watt solar panel) to 4 peak sun hours (using 500 watt solar panel) to get fully charged.

Keep reading…

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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