Why solar batteries may not be charging fully

Fixing the problem of solar batteries are not charging fully can be challenging yet should only be ignored at one’s peril. After all, partially charged batteries don’t last yet batteries can account for up to 30% of of your solar system.

In this post, I will share with you the  signs that show your batteries are not charging fully, tips to both prevent and fix common problems associated with charging.

Signs that your batteries are not charging fully

These are some of the telltale signs that your batteries are not charging fully:

# 1. Appliances run-time on battery reduces

When your appliances work for less than the expected runtime from your battery bank even when your location receives the expected daily sunshine hours.

# 2. Charge controller status never gets to float mode

Your solar charge controller status continuously shows the battery charging status as bulk or absorption- never goes to float mode even after several days of sunshine.

Different controllers display this differently:

  • On some controllers, you have a continuous yellow light showing 50-90% of SoC charge
  • On others, the battery voltage (volts) never reaches float level or absorption voltage – some controllers have an inbuilt voltmeter or you can use an external digital voltmeter to measure the voltage.

Tips to prevent and fix solar batteries not charging fully

With that out of the way, there are several possible reasons that may stop your batteries from charging fully related to any of your solar system components – solar panels, charge controller, appliances and the battery connections.

Let us look at each of the components in turn.

Note: The tips shared below work ideally for a well designed and sized solar system including solar panels, charge controller and batteries sized properly.

Solar panels : How they can affect a battery’s ability to charge

Your solar batteries may not be charging fully because of low performance of your solar panels. There are several possible causes of solar panels not performing well:

# 1. Are you receiving the expected number of hours of sunshine – perhaps your batteries are expected to fully charge with at least 5 hours of sunshine as per design and at this time of the year – you are receiving 3, which is 60% of the expected charge?

# 2. Your panels are covered with dust and other debris and need a clean

# 3. There are shadows cast on your solar panels which reduce the amount of sunshine that your panels are receiving – check that there are no obstacles casting shadows on your solar panels

# 4. Poor panel orientation of your solar system panels- check that they are properly oriented to receive maximum sun for your location

Charge controller : How it can affect a battery’s ability to charge

Your charge controller could also be the reason why your batteries are not charging fully. There are a few things easy to overlook that can affect how well your batteries charge.

Does your charge controller working well? Some charge controller models perform a self-test to confirm that they work well.

If you charge controller has that feature, confirm that the charge controller self-test completes successfully.

If so, then most probably the controller is in a good working condition. Otherwise, check the wiring, and if it still persists, consider replacing your charge controller.

Is the charge controller set up to charge the type of batteries in your bank? Charge controllers need to be set according to the battery type being charged, whether Flooded, AGM, Lithium, Gel.

The charge controller will adjust the settings accordingly so that the batteries are charged appropriately and fully.

Appliances : How they can affect a battery’s ability to charge fully

Sometimes appliances left connected and switched on can drain a battery over time and stop it from charging fully. So check, do you have any appliances connected to the batteries that run all the time – like an inverter and fridge ?

If so, try disconnecting them and check if the batteries charge fully.

Battery connections : How they can affect a battery’s ability to charge

The quality of connections and condition of batteries can also affect how well a battery is charged. For a battery to charge fully, make sure:

  • The wires from the charge controller to the battery are firmly connected to the terminals.
  • Ensure that the battery terminals are clean with no greenish yellow powdery residue on the terminals. The residue restricts the charging current and can stop a battery from charging fully.
  • Do you use flooded batteries or Sealed maintenance free batteries? Flooded batteries need to be periodically topped up with distilled water for them to hold charge.

Hope this helps – If you still have challenges after going through the list, contact a good solar system installer.

Related Topics

Why is my inverter/charger not charging batteries
What can 300W, 1000W, 1500W, 2000W inverter run ?
Inverter buying guide