How Long To Charge 12v Battery With Solar panel? + Calculator

Last Updated: March 3, 2023

Solar panels allow us to convert sunlight into electricity and batteries are used to store that power so we can use it later on.

So to determine how long will it take to charge a 12v battery with a solar panel we need to keep a few things in mind before doing the calculation

Battery capacity
Solar panel size
Weather conditions / how much power solar panels are producing

Here’s how these factors will affect the recharging time

Battery Capacity & Charging Time

Battery capacity is the amount of power that you can store in the battery.

Normally the battery capacity is measured in Amp-hours (Ah) but to make things more clear we’ll calculate the battery Ah into Wh (watt-hours)

because the total power is measured in watts and also solar panel’s power is measured in watts

12v batteries come in different capacity sizes from 5Ah – 200Ah battery. The solar panel size and charging time will vary on the capacity of the battery

here’s a list of different size 12v batteries from Ah-Wh

12v Battery capacity (Ah)	Equals to Watt-hours (Ah*Volts)
50Ah	600 Wh
60Ah	720 Wh
70Ah	840 Wh
100Ah	1200 Wh
120Ah	1440 Wh
150Ah	1800 Wh
170Ah	2040 Wh
200Ah	2400 Wh

For example, if you have a 12v 100Ah battery which will be equal to 1200 watts capacity (Watts = Ah x volts)

This means you can draw up to 1200 watts in a 100Ah battery depending on the type of battery which I’m gonna cover in a moment.

So you’ll need 1200 watts of DC power produced by the solar panel in order to recharge your 100Ah battery.

How Does Battery Type & DOD limit affect the charge time?

there are 3 most common types of 12v deep-cycle batteries (Lead-acid, AGM, & Lithium-ion).

All of these have a different DOD (Depth of discharge) limit. In simple words, how much percent power you can draw from your battery

Lead-acid or AGM batteries have a DOD limit of 50% which means you can only use 50% of the battery’s total capacity otherwise discharging your lead-acid or AGM battery to 100% will damage your battery. But lithium-ion batteries can be discharged by 100%

So if you have a lithium battery and you’re draining 100% every time before recharging so it will take double the time to be fully recharged then lead-acid or AGM same sized battery

What size solar panel for a 12v battery?

After calculating the battery capacity and its DOD limit which gives us the wattage capacity of the battery so now let’s calculate what size of solar panel will do the job

Let’s assume that you’re using a 100Ah lithium battery so you need 1200 watts of total power to fully recharge the battery from 0-100%

Now, what size solar panel you’ll need to charge your battery in a single day? Use this formula to calculate the size of the solar panel for your 12v battery

(100 * 12 / 5) + 20% =  288 watts

So a 12v 300W solar panel will fully charge the 100Ah battery from 0-100% in 5 hours under ideal sunlight conditions or a 150W solar panel in 10 hours

use this website to see the average solar sun hours in your city. I live in Florida so here we receive about 5.8 peak sun hours.

This estimated time is based on if your battery is on rest mode means no appliances are connected to the battery while charging. But if you’re running the appliance with a battery while charging then add up the watts of the appliance into the solar wattage required then calculate the size of the solar panel

What size solar panel for 12v battery – Calculator

What is the maximum charging voltage for a 12-volt battery?

a 12V battery’s voltage input will vary on how much charge is remaining. The battery will consume different voltages during the charging time from 11.5v to 13 volts (although it also depends on the manufacturers)

12-Volt Batteries State-of-Chart & Open Circuit Voltage

Battery State of Charge	AGM batteries	Lead-acid batteries	Gel Batteries
100%	12.8v	12.7v	12.85v
75%	12.6v	12.4v	12.65v
50%	12.3v	12.2v	12.35v
25%	12.0v	12.0v	12.00v
0%	11.8v	11.8v	11.8v

The state of charge or SOC of a battery is the value of how much energy is remaining in the battery

Chart – How Long Does It Take To Charge 12v Battery With Solar panel?

12v Battery capacity	Solar panel size	Estimated Charge time (lead-Acid or AGM battery 50% Discharge)	Estimated Charge time (Lithium-ion battery 100% Discharged)
50Ah	100W	3.7 hours	7.4 hours
50Ah	200W	1.8 hours	3.6 hours
50Ah	300W	1.2 hours	2.4 hours
100Ah	100W	7.4 hours	15 hours
100Ah	200W	3.7 hours	7.4 hours
100Ah	300W	2.5 hours	5 hours
150Ah	100W	11.2 hours	22.5 hours
150Ah	200W	5.5 hours	11 hours
150Ah	300W	3.7 hours	7.4 hours
200Ah	100W	15 hours	30 hours
200Ah	200W	7.5 hours	15 hours
200Ah	300W	5 hours	10 hours

_{How long to charge a 12V battery}

Battery Charge Time Calculator

MPPT vs PWM charge controller efficiency

The charge controller is a device that regulates the voltage coming from the solar panel to match the voltage of the battery.

Watts = Amps x volts. Keep this formula in your mind.

How many volts should a 12v solar panel produce? 12V solar panel will produce 18 volts under ideal sunlight conditions (although it also depends on the manufacturers). as the intensity of the sunlight will decrease also the voltage of solar panels will

so a 12v 100W solar panel under ideal sunlight conditions will produce 18 volts and 5.5 Amps. To decrease the 18V we’ll use a charge controller

So an MPPT charge controller will drop the higher voltage of solar panels but will increase the Amps to match the wattage coming from the solar panels which makes them 30% more efficient than the PWM charge controller and you’ll not lose total watts

but the PWM charge controller will drop down the voltage but the amps will stay the same which makes them less efficient and there will be a wattage loss

So having an MPPT or PWM charge controller will make a difference in the charging time of your battery

How do you charge a 12V battery with a solar panel?

Frequently Asked Questions

How long does it take to charge a 12v battery with a 100 watt solar panel?

on average, a 100W solar panel will produce 80 watts per hour so multiply this number by the number of sunlight hours your location receives using the website I have mentioned above. e.g 80*5 = 400 Wh

Now convert your 12v battery capacity from Ah – Wh by using this formula Watts = Amps * voltage

let’s take a 100Ah battery as an example 100*12 = 1200 Wh

1200/400 = 3 days

100W solar panel will fully charge the 12v 100Ah battery in 3 days with 5 hours of sunlight per day

How fast will a 200 watt solar panel charge a 12-volt battery?

If it’s a 12v 100Ah battery so a 200W solar panel will take 7.5 hours to recharge the battery from 0-100% and 3-4 hours for 50% discharged battery

Can you overcharge a 12-volt battery with a solar panel?

Yes, you can overcharge a 12v battery with solar panels if you’re not using any charge controller. So with the help of a charge controller, you can keep your batteries safe from being overcharged

What happens to solar power when batteries are full?

When the batteries are fully charged then the charge controller will directly supply the power coming from the solar panel to the inverter and will stop sending power to batteries.