Solar Panel Draining Battery: Reasons and Solutions

It’s common to connect a solar battery to your trusty solar panel. But sometimes weird things can occur. For example, your panel deciding to feed on your battery instead of charging it. So why does this happen and what is the fix?

A good solar panel won’t drain your battery; even during nighttime. If it happens the main reason is that its blocking or bypass diodes are broken and need replacement. Even then if you have a Solar Charge Controller it’ll prevent battery drainage.

Usually, most people’s solar panels drain during the night. Due to this most of the time, people think solar charge controllers or inverters are somehow the culprits too. The funny thing is Solar Charge controllers actually prevent battery drainage.

Therefore it’s actually very improbable that your solar panel or other things are the reason why your battery is getting drained. 

In the following article, we will take a good look at the reasons why solar panels drain batteries, faulty conditions that cause such distress, how to fix those conditions, how diodes stop battery drainage, how to replace and various trivial solutions you can try.

Why is my Battery Getting Drained?

The most important query is why does this happen? You may be thinking something is wrong with the panel itself. And you are exactly correct.

Nine times out of ten, it’s the diode that gets broken and creates a situation that makes the current flow in the opposite direction, draining the battery. But even then that shouldn’t happen. Why?

One reason can be the direct connection between battery and panel. Learn more about if you should connect panels and batteries directly.

The short answer, in this case, is no. Your Solar Panel and Battery connection should have a charge controller and this charge controller that automatically stops this discharge so the offender can be broken battery or solar charge controller or other conditions. Here are some good reasons why this fiasco happens.

1. Charge Controller Issues

If your controller is faulty it can mess up the current flow. This can drain the battery fast as stated previously. Remember that there is no power coming into the solar panel during night time but the Solar panel can decide to feed off from the battery if the charge controller is broken

Another issue is if you programmed your charge controller to power up the terminal after the sun goes down. If that is the case please adjust your settings. 

2. Your Battery is damaged 

If you are letting your batteries go to 0% and then charging it to 100%, then there is one bad news for you. 

Your battery is probably damaged. And that right there will ensure rapid discharge from your battery. That’s why recharge the battery at 50% (For Lead Acid) and 30% (For Lithium Ion) mark otherwise it’ll cause problems.

3. Extreme Weather Condition

Extreme weather will break your battery fast. Think about the cold parts of Eastern Siberia. The temperature would cause a malfunction in the internal circuit. So you need some high-end battery that supports a good temperature range in that case.

4. Parasitic Draw

It’s a well-known problem that people often ignore. Even when you shut down your system, your battery is getting drained. Just like TV in standby mode keeps using power. This especially is an important case if you are living off-grid and your appliances use solar power.

5. Internal Problems

If everything is set up all right maybe the problem is your solar panel or its wiring problem. Maybe the panel is old or the diode is broken. Or it’s a cheap, bad-quality product. Be sure to check the wiring of your solar panel.

Do Solar Panels Drain Battery at Night?

A very common question asked by many. The answer is yes. Solar panels will discharge at night if your solar panel doesn’t have a diode or it is broken. In fact not only does it happen at night, but it also happens when the panel doesn’t get sunlight. Why you may ask. 

Well at night your Panel Voltage becomes 0. And without diodes and charge controllers the current reverses its path. And your battery gets drained. We’ll discuss more info regarding Diodes in a later section.

Solution to Solar Panel Draining Battery

So now you have a problem and as we told you we’ll be providing a couple of optimal solutions for each case. More descriptive solutions are given below.

1. Solution to Charge Controller Issue

A good thing you can do is reset your charge controller. Here you have to keep in mind two types of reset, a hard one and a soft one. But first, try the soft one before moving on to the hard one.

You should have a reset button to restart your charge controller. Do keep in mind that some model needs you to press both power and the reset button or four buttons at the same time. 

Your screen will blink and flash and it will return to the display screen soon after. It is basically like rebooting your pc or mobile phone.

Now hard reset. Always do it at night. Disconnect the battery first, then the panel. Wait like three to ten minutes. Now reconnect the wires. It should be in the same order you disconnected them. And viola, hopefully, it will fix your charge controller issues.

2. Solution to Battery Issues

It is highly recommended that you replace your battery if you think it is broken.  Also, take good care of the battery. Do not overcharge it or let it sit idle. Remember to use quality batteries. And always remember battery voltage should be less than panel voltage.

3. Solution to Extreme Weather Condition

The best solution is to buy equipment that can withstand the temperature and the weather of your current location. Also, prevent conditions such as shading or overheating that can mess up internal circuits and cause battery drainage.

4. Solution to Parasitic Draw

If you are living off-grid, the best thing to do is to connect your battery to an independent panel not connected to any other thing. Other than that monitor your appliances connected to the panel. Thoroughly check if unwanted equipment is eating up the battery. 

5. Solution to Internal Problems

For internal problems, you have to replace your broken equipment. Also, be careful while choosing products. Don’t buy cheap low-quality products or you will face the same problem. If possible, refrain from using old products. If something is broken don’t hesitate to contact an electrician or your solar company support. 

Solar Panel Diodes and Their Role Stopping Battery Drain

So what are diodes? Basically, current flows in a circuit from high voltage to low voltage. So current can flow in both directions. Our little semiconductor friend here will make sure the current only flows in one direction. So how is this related to battery drainage?

It’s pretty simple. When your panel gets sunlight it has more voltage than the battery. So current goes from panel to battery. But when there is no sun (For example nighttime), the voltage of the panel becomes zero and the problem starts to occur.

Current flows from Battery to Panel thus draining or discharging it. The diode here will make sure the current only flows from the panel to the battery. So a working diode will stop the draining.

How to Replace Solar Panel Diodes and Fix Draining

So your diode is broken? How do you replace it? Your best bet is to hire an electrician to fix it for you. But sometimes it’s not possible outright. So here is a short guide on how to replace the diode of your panel. Be sure to be careful with electricity

  • Step 1: Take a screwdriver, a small slotted one. Now locate the junction box of the panel. It’s on the back side of the panel. 
  • Step 2: Now with that screwdriver open the cover of the junction box by prying the cover locking tabs
  • Step 3: Identify the diode that requires replacement. You can spot the tip of the solder iron under the lead of the diode. Now remove the diode from the terminal by using the tip of the solder iron and lifting each lead of the diode separately 
  • Step 4: Any excess solder will have holes in the junction box terminal. Clean them
  • Step 5: The Leads on the replacement diode should be bent to ‘U’ shape. If not, bend the lead in the same manner (You can use a Plier). It should be like the lead you just removed in step 3.
  • Step 6: Install the diode in the terminal hole. Pay careful attention to the connection. The gray bar or the band side of the diode should be oriented in the same direction and on the same side as (+) Positive cable gland.
  • Step 7: Now solder the intersection of the diode lead and terminal carefully
  • Step 8: Close the junction box cover. Don’t forget to apply pressure to the locking tab to seal it shut.

You can check out a more detailed guide here.

Tips on Fixing Solar Panel Draining Battery    

Aside from Diodes, there are also many things you need to be careful about; such as Solar Charge Controller, Battery Maintenance, etc. So here are some more tips regarding fixing these issues:

  1. Restart the Charge Controller. As with many electronics a soft or hard reset can fix many problems. So try that and it might help.
  2. Check your wiring. If your wiring is torn or broken, it’s time to change it. Faulty wires affect battery charges and cause other weird issues, so fix it fast.
  3. Use a multimeter to check if your battery is dead or broken. If that’s the case, you have to get a new battery.
  4. If you are living off-grid, your battery will be draining because of your appliances. It’s natural. But be sure to calculate the correct number and check if your battery is not draining more than it should. Unplug some devices if it’s draining too much.
  5. Ensure that you have weather resistant equipment if you live in places with extreme weather. It’ll stop causing various malfunctions.
  6. Recharge your batteries in the correct ways and take care of them. If you don’t, problems like these will occur very often.
  7. If you are using more than one solar panel to charge batteries consider By-Pass. It’ll provide a good versatile connection in various situations.
  8. Buy decent quality solar panels and try to use relatively new panels. Not only do they tend to have good diodes but also good overall features that will help prevent issues.
  9. A Good Overall tip is to regularly inspect your system. Inspection can solve many problems regarding batteries and panels and stop issues like this.
  10. If all else fails, hire experts or electricians. Nothing beats practical experience after all.


Solar Panel Draining Battery is a common yet quite a tricky problem to solve. There can be many causes from battery problems to diode problems. So there are various things to consider. 

But the overall thing to keep in mind is if a solar panel is draining a battery it’s mainly because the diode of the panel is broken. Otherwise, the solar charge controller has faulty settings, the battery is damaged or there are problems with the wiring in the system.

In any case with enough knowledge, you can easily solve most of the problems. And I sincerely hope that you have learned a thing or two from this article and managed to fix your problem.