A battery’s state of fee is a portion that mirrors the quantity of energy it stores relative to its capacity. It provides information on just how much strength it has actually left in ~ it and the approximate time the can provide a sustainable power.

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Understanding the battery’s state is crucial to a battery’s upkeep or maintenance since it can be a basis the tells if the cell is poor or not.

There are several methods to recognize the state of charge of a battery, but only one stands out once it concerns accuracy. The is the technique of identify the details gravity of the cell, which provides a hydrometer.


What is the hydrometer analysis for a totally charged battery? A totally charged battery should have a hydrometer analysis of that electrolyte’s details gravity in ~ the variety of 1.265 to 1.330. The is relying on the type of battery and the manufacturer that the battery.

Although Battery Council worldwide or BCI mentioned that the certain gravity that a fully charged cell is 1.265, part manufacturers like 1.280 or more. The particular gravity that a totally charged battery additionally varies ~ above the battery application, which additionally varies according to the meant cell performance.

Deep bicycle batteries have actually a details gravity between 1.270 and 1.305. Other factors influence the worth of specific gravity, choose the acidity of the electrolyte and also ambient temperature. This is why the right time to carry out a particular gravity test once the battery is totally charged and also rested around three to 5 hours.

This gives the electrolyte within the cell enough time come stabilize, i m sorry will bring about a much more accurate reading. Again, if a battery is completely charged, her hydrometer should read a particular gravity that 1.265 or more.

For submarine lead-acid batteries, the many accurate means of telling its state of fee is utilizing a hydrometer and also measuring the electrolyte’s specific gravity. V the particular gravity analysis on hand, it will certainly then it is in looked on a chart that will have the information around its state of fee equivalent.

How Batteries job-related in relation to the specific Gravity

When a lead-acid battery is in the charging state, its operation is to obtain charge the it will save on its key within. In ~ this state, the electrolyte additionally accumulates an ext sulfuric mountain that makes its acidity more potent.

Due to this, the acid’s thickness within the electrolyte becomes denser than water, enhancing its specific gravity.

On the note, the higher the battery’s details gravity, the far better the state of fee it will certainly have. When checking a battery’s particular gravity, the procedure will require you to gain a analysis from every one of the battery cells.


This means that friend will have several interpretations, and with that said, girlfriend will be able to see the state of fee of every cell. And then, you will certainly be taking the readings and compare it come a chart to check out the state the charge.

The typical State of charge and particular Gravity graph from BCI

As I pointed out earlier, after acquiring the details gravity analysis of the battery, friend will have actually to examine that analysis on a graph that will certainly tell the approximated state of charge.

Here’s a table with the conventional values native the Battery board of directors International. This chart shows the standard values because that two-volt, six-volt, eight-volt, and also twelve-volt batteries.

The readings on the table are based upon 78°F temperature, where the cells are rested because that twenty-four hours.

The table below shows the open-cell voltage or remainder voltage of every cell and also the equivalent details gravity as well as the state the charge.

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Credit for Battery board of directors International

You have to remember the there are several components that may influence the details gravity reading on a battery.

And one of these components is temperature, both the approximately temperature and the temperature the the electrolyte can adjust the readings. That is why the is recommended that the battery is rested prior to carrying out the test.


How the Electrolyte Temperature impact the details Gravity Readings

The electrolyte temperature has actually a direct relationship v the particular gravity the the battery, leading to inequalities in the analysis on hydrometers. When the electrolyte gets colder, it i do not care denser, which likewise raises the specific gravity.

On the various other hand, once it it s okay hotter, the electrolyte is lighter, i beg your pardon decreases the particular gravity. To gain a better picture of these changes, this is a table to refer to.

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Other components that Can affect the specific Gravity Readings on a Battery

Apart indigenous the state of fee of the battery, voltage, and also temperature, several components can also lead to inaccurate particular gravity readings.

Stratification is one of these other factors that have the right to lead to inaccurate hydrometer readings. This is a condition where the battery electrolyte has actually a layered concentration, which limits its capacity to it is in efficient.

This problem usually leader to sulfation, which is one of the leading causes of a battery’s death due to the fact that it prevents it native storing charge.

Higher acid potency on the electrolyte of the cell also raises the remainder voltage that the battery, which can transform the hydrometer’s reading.

However, once carrying out a particular gravity the you need to keep in mind, the general dominion is come let the battery rest for in ~ least four hours come twenty-four hours before testing.


Proper method of using a Hydrometer come Get certain Gravity

In case you need to lug out a particular gravity check on her flooded lead-acid battery for maintenance purposes and you nothing know-how.

Here’s a guide on how to usage a hydrometer and a action by step overview of the entire process. Allow me walk you with each action and aid you successfully bring out the operation.

1. Equip the appropriate Safety Gear

Since you space going to transaction or work-related with a wet cabinet battery with hazardous elements involved, the an initial thing you have to do is come make certain that friend are protected by wearing security goggles and also a pair that rubber gloves.

You additionally have to procure a trustworthy hydrometer to be sure that you space going with each step smoothly.

2. Prepare the Battery because that the certain Gravity Testing

The following thing you need to do is prepare the battery through placing that on a level surface and removing every cell’s lead. Location all the sheathe aside because you will certainly be instead of them when you room done v the process.

3. Warm the Hydrometer Up and also Observe Electrolyte Coloration

Start v one cabinet of the battery and also then attract some electrolytes to the instrument. Yet do it several times to heat the an equipment up and adjust with the electrolyte’s temperature.

After that, research the color of the electrolyte, if it has actually a brown or gray coloration, that means the battery is dying.

4. Start acquiring Readings of the specific Gravity

Draw electrolyte samples to the instrument with a complete dosage till the rise of the tool is floating freely. Host the instrument at eye level to check out where the battery liquid meets the range of the device. Make sure to take keep in mind of the reading.


5. Correct the analysis With the Temperature Correction

To obtain a an ext accurate reading, make certain to include or subtract 0.004 on the analysis for every 10° F or 6° C the electrolyte temperature is above the regular basis i beg your pardon is 80° F or 27° C.

Then from there, note the analysis for the first cell then proceed with the others, law the same. Once you have every one of the readings for each cell detailed and corrected, you deserve to compare them v the table offered earlier.

Based top top the table and the readings friend got, you have the right to tell the state of fee of the battery and see if other is wrong v it or not. Simply make certain that the battery is fully rested before carrying the end the process.

Final Thoughts

That is exactly how you use a hydrometer and see the state of charge of a submarine lead-acid battery. All of the information disclosed above will also allow you to find out everything around the certain gravity, state of charge, and also voltage.

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Just remember, a completely charged battery should have a hydrometer analysis of 1.265 specific gravity or more.