How To Test Rechargeable Batteries

After using rechargeable batteries for a while, you may begin to notice slight changes in the way they perform. These aren’t batteries that you can just toss away like their Alkaline counterparts, because there might be nothing wrong with them.

Impeded performance can happen for several reasons, which are why most people opt to test their rechargeable batteries. The result is used to determine whether or not they should have their rechargeable batteries replaced.

So how can you test your rechargeable batteries to ensure that their battery capacity is still at optimal levels? We will walk you through this while making it as easy as possible for you to understand.

Using A Multimeter

Using a multimeter is quite simple, just follow the steps below.

  • Charge the AA rechargeable battery for the stipulated amount of time stated on its package. To ensure that you get a proper charge make use of its approved battery charger.
  • Break out your multimeter and proceed to make adjustments on the measurement dial. These adjustments are necessary to measure the direct current of the rechargeable batteries. While adjusting your multimeter, ensure that you set it to at least, the highest number of volts your rechargeable battery can provide.

For instance, if your AA batteries have a 4-volt capacity and your multimeter has a 7-volt capacity, adjust the dial on your multimeter to measure 7-volts.

  • Use the metal tip of the multimeter’s negative (black) probe to the negative terminal of your battery, and metal tip of the positive (red) probe to the positive terminal of your battery.
  • You will observe that the multimeter will give you a reading of your battery voltage on its display panel once these probes are connected. Keep in mind that if the battery voltage displayed is lower than the expected capacity at a full charge, then your battery is nearing the end of its usefulness.
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Using Commercial Battery Analyzers

When it comes to Nicd and Nimh batteries the best way to test their battery capacity is to connect them when fully charged to an accurate constant load and pay close attention to their voltages as they discharge.

The battery capacity refers to the amount of load current on the battery, multiplied by the amount of time this load current is sustained for.

Please note again that when testing your rechargeable battery, you must do so with the battery fully charged. When applying this method, you can only use a resistor to perform the function of a load, a stopwatch, and a voltmeter. 

However, we recommend that you make use of a commercial battery analyzer. We recommend the Midtronics MIDMDX-700P-HD HD Battery/System Analyzer with Integrated Printer. 

Keep in mind that you can always get a cheaper battery analyzer for as low as $200. The price of a battery analyzer is based on your budget and what kind of features you are looking for.

However, we must point out that cheaper battery analyzers have limited customization options and accuracy, while expensive battery analyzers give you more options to test different batteries at once.

When using a commercial battery analyzer to test your rechargeable battery, the first step is to have a  connect a power source connected to the analyzer. 

The next step would be to select the kind of battery being tested or simply specify the conditions under which the battery is being tested. Furthermore, you are required to connect the battery which you want to test to the analyzer.

Hit the start button and set both the battery and analyzer down for some hours.

What the battery analyzer does is discharge your rechargeable battery while measuring its discharge time before recharging the battery. You will be able to see your battery capacity when the discharge is complete. 

Using Constant Rate Discharge Testers

Discharge testers are mainly used for deep cycle batteries and are designed to monitor their battery capacity.

How discharge testers work, is by having your batteries discharged at a pre-set current until your battery drops to the pre-set disconnect voltage. However, you need to keep in mind that this process can take a while to be completed.

Using Battery Hydrometer

A battery hydrometer is used to determine the state of charge in a lead-acid battery cell by measuring the density of the electrolyte. To get the density of the electrolyte, the specific gravity of the electrolyte is measured. The electrolyte in batteries becomes denser in response to the concentration of sulphuric acid.

Before carrying out a hydrometer test, please ensure that you have the necessary protective equipment, such as:

  • Googles – For eye protection.
  • Rubber Gloves.
  • Rubber apron.
  • Closed-toe shoes.

Also, battery acid is very corrosive and will dissolve any form of cotton fabric on you. Therefore, you need to makes that you have none on you before carrying out the test. Now, to carry out a hydrometer, follow the steps below: 

  • Have some electrolyte drawn into the hydrometer a few times. This allows the thermometer to adjust to the temperature of the electrolyte; make sure you record the reading.

Take note of the color of the electrolyte. If its color is brown or gray, this means that the battery is defected and is at the end of its life.

  • Allow the float to move freely by drawing a full sample of electrolyte into the hydrometer.
  • Keep the hydrometer in a vertical position at eye level, and take note of the reading where the electrolyte meets the scale on the float.
  • Four points (.004) should be added or subtracted from every reading, for every 10 Fahrenheit that the temperature of the electrolyte is above or 80 Fahrenheit below.

Make adjustments to the reading so that it conforms with the temperature of the electrolyte. 

  • Test each cell and take note of the readings (which should be corrected to 80 Fahrenheit). If there is a 50 point variation between two cell readings, this means that there is a problem with such cells.

The specific gravity of an electrolyte decreases as the battery ages. However, if all the cells of such batteries are with 50 points of one another, then there is no need to have the battery replaced.

We hope this article has been relevant in helping you figure out how to test rechargeable batteries. For a more visual approach, please use this video as reference:

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