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How to know if a solar battery is in poor condition?

In this article I will explain how to tell if a solar battery is in poor condition. Batteries are an important element in many solar installations. Also, unlike other elements, many batteries require maintenance to ensure optimal performance for years.

Misuse of batteries or the passage of time can cause them to stop working as expected. When the time comes, you will need to know if your solar batteries are charging well or if there may be a problem. In this article we explain how to do it.

Methods to know if a battery is in poor condition.

Maintenance and usage (discharge rate) are important aspects of batteries. A battery that is properly used and properly maintained can extend its useful life much more than a “battered” battery with very deep and repeated discharge cycles and without maintenance.

For example, non-sealed monoblock batteries or stationary solar batteries require us to check the level of the electrolyte in the vessels, maintaining the level indicated by the manufacturer (always adding non-acidic distilled water). There are other types of batteries, such as AGM or Gel batteries that do not require this maintenance but need a review from time to time, since failures can occur in the communicating vessels, affecting the performance of the batteries.

These failures can reduce the charging capacity of the battery, also causing it to discharge much faster. That is why it is important to know how to check a solar battery, whenever we suspect a malfunction or an inverter warning is triggered.

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To carry out this routine check, you only need two tools that will allow you to verify if there is a problem: the hydrometer and the multimeter.

Measured with the hydrometer (Batteries with maintenance and liquid electrolyte type OpZs or similar).

The hydrometer is a small device that allows you to measure the density of the electrolyte (know when a battery needs liquid). It may have different shapes but its operation is similar for all models, and you may find it as part of your solar battery maintenance kit. In the case of outdoor glass batteries, it usually indicates the density of the electrolyte when it is at 25ºC. and fully charged normally between 1.24g/ml and 1.26g/ml.

With the hydrometer you must measure the densities of each glass of the solar battery, ideally when it is charged and at rest. If the battery works correctly, the density of all the cells will be practically the same, which is the desired result. Therefore, it is not necessary for you to know what the ideal value of that density would be, if they are very close to each other it will be enough, unless you obtain a very low density of less than 1.20g/ml once the loading and resting process is finished. .

If one of the cells of the battery has a lower value of density, so that the hydrometer floats very little, there is a good chance that that glass is damaged and therefore that battery does not work well.

Measurement with the multimeter.

A battery or glass in poor condition goes up in voltage as soon as we charge it but also goes down in tension as soon as we ask for energy, basically it is not storing energy. For this reason, the measurement exclusively of the voltage is not, in itself, an indicator of the state of the battery, unless the average voltage is very low.

With a multimeter (voltmeter) or tester we can also check the solar batteries. To do this, each battery must be measured separately. This way you will be able to identify which batteries/glasses are in good condition and which one is in poor condition.

The voltage measurement will tell you if the battery is charged and working or if it may have some kind of problem. The specific measurement values ​​that you must take into account are the ones that we show you in the next point.

Reference voltages for charged batteries.

Checking the status of a solar battery or its level of charge is simple and can be done by measuring its voltage. It is best to consult the technical documentation of each battery to find out this information from the manufacturer, but if you do not have it, you can take the values ​​shown here as a reference.

Reference voltages for charged batteries.

The charge level of the battery itself is an important indicator of its condition. The batteries when they are charged and at rest, that is to say without external elements charging, have very similar voltage levels that we can take as a reference to carry out this check:

  • 12V battery: 12.5-13V
  • Battery at 24 V: 25.5 V
  • Battery at 48V: 50.9V

If we measure the batteries and the voltage value is similar to the ones we just mentioned, it means that the battery is charged and in good condition, except that when we demand these values ​​drop quickly. However, if we see that it gives us a strangely low value, it is indicative that the battery is in poor condition or is defective.

Voltages that may indicate battery failure.

Care must be taken as values ​​slightly lower than those shown above may simply indicate that the battery is discharged, but that it is in good condition. Next, we leave you some reference values ​​from which we can understand that the battery is damaged, always at the end of the charging period and at rest:

  • Battery at 12 V: 11.5 -12 V or less
  • 24 V battery: 22 V or less
  • 48 V battery: 44 V or less.

To suspect a battery failure, it is necessary to detect values ​​like the ones we have just shown you, that is, very low. For example, if we obtain a measurement of 11.5 V in a 12 V battery, it means that the battery may be in good condition, but discharged. Knowing the voltages of your battery model and accompanying the voltage measurement with a density measurement will make it easier for you to find problems in your solar battery.

Remember that the voltage value to be used is that of the battery itself, measured with the multimeter, and not the one indicated on the charge regulator during the day. The value that appears in the regulator can be distorted if at that moment the solar panels or a generator are injecting energy. To be able to consider the voltage value displayed on the regulator as reliable for assessing the state of the battery, you must: wait at least 2 hours after sunset and make sure that there are no other external power sources active (such as a generator), or sources of consumption.

When a battery in poor condition is detected, it is recommended to carry out a slow charge using a battery charger until fully charged. Once the battery is charged, it will be reconnected and it will be observed how it evolves. If this battery is discharged again in a short time, it will be confirmation that it is damaged.

In the market there are also what are called ” battery testers “, there are better and worse, however the basic operation is that the maximum current that the battery can give is programmed and a start button is given, giving a verdict. What it basically does is short circuit for a short period of time, analyzing current and voltage. Based on these data gives a verdict. However, they are only approximate methods. The best method is always to discharge the battery, after charging it, counting the Ah removed from the battery, and comparing it with the technical specifications of the battery/cell itself.

If you need professional help for your solar batteries.

By performing the checks with the voltmeter and hydrometer, you can easily know if your battery is in good condition and its level of charge. In any case, if you do not know how to check the solar batteries of your installation or you are interested in any of the ones we offer on our website, you can contact us.

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