Why is my inverter shutting off due to "battery low voltage"?

Why is my inverter shutting off due to "battery low voltage"?

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Both our standard inverter and hybrid inverter/chargers have low voltage protections. In a hybrid inverter, you may get warning about "battery low voltage" or "battery over-discharge", and in a standard system your charge controller and inverter may show a fault or shut off due to low battery voltage.

This cut-off is designed to happen when the batteries have been discharged too low, to protect the batteries from being irrecoverably damaged. Learn more about battery maintenance here. If this has happened there is a chance the batteries have been damaged already, and the first thing you should do is recharge the batteries back to full as fast as possible - make sure you switch off the breaker between your batteries and inverter.

If you are using more power than you are producing, you will eventually draw the batteries low enough to reach the cut-off point. This can take several days, or only a few hours, depending on how much of an energy deficit there is. 
In this example, the batteries start fully charged with a capacity of 9600wh: 


Energy Produced 

Energy Consumed 

Energy Deficit/Surplus 

Battery Level 





9600wh (100%) 





9000wh (94%) 





8700wh (91%) 





8800wh (92%) 





7700wh (80%) 





7000wh (73% 





6200wh (65%) 





5400wh (56%) 





4400wh (46%)



In this example takes 9 days to run into the BLV fault. 

It can be difficult to then get the batteries back up to a full charge during cloudy weather as the panels are putting out much lower power. In this example, with the panels putting out around 300wh a day, it will now take 17 days to get the batteries back up to 100% charged, with no appliances running off the system. 
This means it is extremely important to keep an eye on both the battery levels and the weather report, especially when you are new to off-grid solar, and to make sure that you don’t get into a situation where you have less and less energy stored in the batteries at the end of each day. 

Reading battery levels:








These tables provide a good way to estimate the amount of energy stored in the batteries. 

The voltage needs to be read when there is no current (amps) going into the batteries - this means there is nothing drawing power from the batteries or charging the batteries. 

If there is current going into the batteries, the voltage will read higher than the true internal battery voltage. This is because the charge controller is applying a charging voltage to the batteries to charge them. 

When there is a current being drawn from the batteries, the voltage will read lower than the true internal voltage of the battery, as there is a voltage drop over the internal resistance inside the battery. 

Therefore, if you are trying to determine the current state of battery charge, you need to read the voltage when there is minimal current entering or exiting the batteries. 

Often the best time to read the battery voltage is just after the sun has gone down, as that way you can make sure there are no appliances running and there is no incoming charge current from the panels. This will give a more accurate indication of the internal battery voltage. If you are not able to take a reading at this time, you can also flick off the circuit breakers from the solar panels and to the inverter, then wait ten minutes for the voltage to stabilise before you take a reading. 

Other possible causes 

If you have read through the previous information and feel like your batteries are still not holding as much charge as they should, then there are a few other things to check. 

Battery imbalance 

Please check the individual voltage of each battery using a multimeter - they should all be close to 12.8V when fully charged. If any battery is more than 0.5V higher or lower than the other batteries, this indicates there is an imbalance. 

This imbalance can be caused by a few things: 

  1. Running 12V appliances off a single battery in the battery bank instead of using a 48V or 24V stepdown 
  2. Frequent over-discharging of the batteries 
  3. Large temperature difference between the batteries 

    The first thing to do is to rebalance the battery bank by charging the batteries individually with a 12V charger or using a battery equalizer. If the same battery continues to develop an imbalance, please contact GridFree to discuss your options. 

    Loss of battery capacity 

    If it has been confirmed the batteries are reaching a full state of charge before the end of the day, there is no imbalance, and there are no significant loads on the batteries, yet they are still discharging quickly overnight, this is a sign the batteries have a reduced capacity. 

    The most common cause of a decrease in capacity is from insufficient re-charging of the battery bank. If the batteries are left in a partially charged state, the lead plates in the battery will degrade and will not hold as much energy as when the batteries were brand new. 

    If all individual batteries read the same voltage at all times and have a reduced capacity, it is not possible for this to be a manufacturing defect and is very unlikely to be covered under warranty. However, we encourage you to please contact us, and we can discuss your options.