How to Connect a Solar Panel to a 12V Battery?

In this article, I will explain how to connect a solar panel to a battery step-by-step.

I will also share a few tips you need to know along the way.

Here is a diagram connecting a single 100W solar panel to a 12V 100Ah lithium battery and a 500W inverter:

Connecting a solar panel to a battery and inverter

Step 1: Connect the battery to charge controller

In the first step, you will wire the battery to a charge controller. It is essential to wire this component before you wire the solar panels. If you wire the solar panels to your charge controller first, the fuse of the charge controller might blow.

If your charge controller has no replaceable fuse, you can’t use it anymore.

Always connect your battery to the charge controller first.

Read more: Can I connect my charge controller directly to an inverter?

The thickness of the wire will depend on the type of charge controller you get. If you get a 20 amp charge controller, you need to use a wire thickness that can carry 20 amps without overheating (AWG14 / 2.5mm² or bigger). Flexible wires with a nylon coating are preferred (THWN-2 cable). Learn how to select wires and thicknesses in my book.

The manual of the charge controller will also suggest a wire size and a fuse size.

You need to keep these wires as short as possible because they will be expensive.

Step 2: Wiring the Loads

The following step is to wire the loads. These can be an inverter, 12 volts dc box or both. You have two options here:

  1. Attach the loads to the charge controller output terminal
  2. Attach the loads to the battery terminal

Option 1:

Only use this option if you have a small DC load. These terminals cannot deliver high currents but will protect your battery from over-discharging.

For example, the renogy rover 20/40Amp series, can only supply 20 Amps at its load terminals both for the 20 amp and 40 amp version. You can only attach 240 Watts (20 amps x 12 Volts) to the load terminals. You see that this is very limited. It’s not enough to connect an inverter to it.

DC fuse box attached to the load terminals of a charge controller
DC fuse box attached to the load terminals of a charge controller
Never attach an inverter, battery charger, or a device that draws a lot of current (amps) to the load terminal of a charge controller.

Option 2:

If you have a device that can draw a lot of current, like an inverter or battery charger, you must attach the wires directly to the battery terminals. From here, you can wire it directly to the inverter or to a busbar. See the following diagram for reference:

charge controller connected to battery and loads
Charge controller to battery and loads

Using this setup, you have to monitor the battery levels. Use a volt meter in case of lead-acid and a shunt for lithium batteries.

Before the next step, ensure you have programmed your battery type in the charge controller. This will be explained in the manual of your chosen charge controller.

Step 3: Connect solar panels to charge controller

The final step is connecting the solar panels to the charge controller.

If you have more than one panel and are unsure if you need to connect it in series or parallel, check out my article here, or if you have two solar panels and one battery, check out the wiring diagrams here.

Are you confused about the specifications of the solar panel you got? Check out my article, where I explain all the parameters of a solar panel here.

Use the cables that come with the solar panel, which are UV-resistant. Other cables will crack and break over time when exposed to UV radiation. This is the part when you need to oversize the diameter of the wire to account for voltage drop. Try to keep the voltage drop under 3%. Click here to calculate the voltage drop.

What is voltage drop?

Voltage drop occurs when a long cable delivers energy from point A to point B. The cable’s length increases the cable’s resistance, reducing the voltage at point B.

For example, your solar panel delivers 18 Volts DC and 5.8 amps to the charge controller, and the wire length is 40 feet.

how to calculate voltage drop
Voltage drop in a single panel system

As you can see in the calculation, the voltage drop is 4.09%, reducing the overall power delivered to the charge controller.

Let’s calculate the amount you will lose:

0.74 volts x 5.8 amps = 4.3 Watts

This is not much, but it can add up quickly with multiple panels. In your country, it could be that the voltage drop may not be above 3% by law. To reduce the voltage drop, you use thicker wire.

Try to limit voltage drop to 3% because it will increase power loss in the system.

The final version will look like this:

Complete schematic of how to wire a solar panel to a battery with loads attached
Complete schematic of how to wire a solar panel to a battery with loads attached


You need to have fuses in between your devices. The main objective of having fuses is to protect the wires from overheating or catching fire, not to protect the device. This is because you will size the wires to the amount of current that can flow from one device to the other.

You need fuses in the following places:

  • From battery to the charge controller
  • From battery to inverter
  • From battery to DC fuse box

Check out my article on how to calculate fuse sizes. This is also something I write about in my book.


You have come to the end of this article. Hopefully, you know how to connect a solar panel to a battery.

If you have questions, please write them in the comment section below.


Can I connect a solar panel directly to a battery?

No, there is no way for the solar panel to stop charging the battery, resulting in overcharging the battery.

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18 thoughts on “How to Connect a Solar Panel to a 12V Battery?”

  1. Hi, do you need to match the voltage of the solar panel to the battery?
    So a 12v panel for a 12v battery? Or can the panel be 18v or 36v etc.

    • Hello Rob, you do not need to match the solar panel to the battery. The charge controller will take care of the voltage transformation. For example, you have an 18 volts panel connected to a 12 volts battery. The charge controller will transform the 18 volts down to the ideal voltage to charge the battery. Do not forget to adjust your charge controller to match your battery pack voltage.

  2. Hi, are you saying if you dont wire the load direct into the controller the battery level will not be accurate on the display? If that is the case, how does the controller know when the battery is depleted, for it to know when to charge? Thanks, bit confused!

    • Hello Joe, I’m not sure if I understand your question correctly but I will try to answer.

      – The charge controller is there to stop your battery from overcharging. If you keep putting energy into your battery it will damage the battery and it might catch fire.
      – The charge controller is there to disconnect the loads from the battery after your battery reaches a certain low voltage. This is to protect the battery from draining completely. If the battery is drained completely, it will damage the battery.

      I hope this answered your question.

    • Hello Mimi, a shunt keeps track of how many Ah you have left in your battery. It takes into account the Ah that goes into the battery and the Ah that goes out of the battery. That way you know exactly how much % charge you have left.

  3. Once the controller is set up by hooking the battery then hooking the panel and you have it all put together, Can you just hook up the battery to use it and unhook it when its not in use..?

    • Yes, you can disconnect the battery when it’s not in use. However, why would you do that? It’s good to have a trickle charge into your battery to keep it topped up.

  4. Can you use both option 1 and 2 at the same time. Low amp load connected to the Charge Controller, say usb outlets and Hi amp load direct of the battery, say 12v kettle?
    To add to this I want to use the battery as the slave battery in a dual battery system

    • Yes, You can use the load output of the charge controller and have other loads connected to the battery. The user manual of the charge controller will tell you how many amps you can draw from the load output. Don’t forget to fuse the outputs.
      If you want to use another battery, that is separate from your existing battery I recommend a battery to battery charger. Renogy has a good one.

    • Hello Kitso,
      Put your 4 12V batteries into series. That will make it 48Volts. Then wire the inverter to the batteries. Don’t forget to add a fuse in between.

  5. On my RV, I have currently a charge controller and one 12V battery. I would like to add another 12V battery into the mix. Do I have to do anything to my charge controller, and how do I know if my charge controller is capable of handling two 12V batteries. As well, I would like to add additional solar panel. Right now I have two 50 for a total of 100W.
    One more question. What should I look at when buying a battery for my system?

    Thank you


  6. Hey Nick, are you aware of any solar controllers that have a load output circuit that ‘outputs’ without a battery connected to the system?

  7. How would this system translate if you were using the solar panel to recharge modular large batteries which are then put into a device after being recharged… how would it be restructured if the batteries were not directly linked to the load during recharge?
    Hope this makes sense.

    • I assume you mean you want to recharge cordless drill batteries? You will need a small battery in between, because the charge controller needs a battery to function. If the charge controller has the charging specs for your modular batteries, then you can set it like that. However, I doubt it will be in there.


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