Testing and Buying Used Batteries

 

For use in residential UPS (uninterrupted power supply) or solar systems, using batteries can save up a lot of costs. But there are some things to be considered before going for a used battery.

Testing of Batteries

It is a simple task to test a battery but a very important one as it can tell you a lot about the battery, especially in purchasing used batteries. In simple terms, it is a two-step process with some initial tools required beforehand.

·         A load that can draw current and drop voltage across itself

·         A digital or analog voltmeter (digital is a better choice because of its accuracy)

·         A hydrometer is typically used to check the gravity of acid in batteries

Now the first step requires you to use your voltmeter. Measures the voltages of the battery without any load connected and record the reading. After this, connect the load using jumper cables to the said battery, check the voltage again. You are looking for no change in reading; if you see a change, several things like one of the cells are damaged.

For the second step, you need to connect the Hydrometer to the battery. The Hydrometer is for testing the state of charge of the cell of the battery. This is done by measuring the specific gravity of the electrolyte, in turn finding out the density of the electrolyte. The higher the acid concentration, the denser the electrolyte, and greater density mean the greater state of charge.

You need to be very careful while using a hydrometer. You would be handling very strong acid, and there are some professional safety guidelines set to ensure no problems while performing this test. You should have rubber gloves, a rubber apron, closed-toe shoes, eye protection, and most importantly, don’t wear cotton clothes as sulfuric acid will dissolve the fabric if it comes in contact with it.

One thing to keep in mind before performing this second part of the test is that the hydrometer test should never be done if the battery is recently watered. This is because it needs at least one cycle of charging and discharging before the electrolyte can mix completely with the water.

Buying Used Batteries

After testing a few suitable batteries and separating them from the rest, you need to determine what you need the battery or batteries for. In the case of UPS or Solar inverters, you need to look for the total voltage and current required by you. There are data plates on everything these days and what you need to do is look up the currents required for all the devices you want to power by these batteries. As everything will be in the series connection, you can add up all the currents to get the total required current. Typically your battery or battery bank should provide about double the value of the total current required by you. This will give you the longest life of the batteries. So after making a suitable battery bank that is enough to power your system, you are set.