Charging Systems- Battery Testing

Battery testing

Before testing any battery you must go through a few simple steps/ tasks to make sure the battery is okay for testing. Firstly you must inspect the battery specifications, these are-

·         The make of the battery

·         The battery number

·         Battery capacity in cold cranking amps (CCA)

·         The type of battery (conventional, maintenance free, gel cell, orbital, etc..)

·         Whether you can get to the electrolyte.

Next you need to carry out visual checks, these include-

·         Are the terminals clean and tight?

·         Does the battery show signs of swelling?

·         Does any further action need to be taken?

Now that you have carried out these checks you can start to test the battery. The first test is checking the electrolyte levels in each cell. To do this you must first obtain a pair of safety glasses, and gloves as the electrolyte in the cells can cause severe damage, if it comes in contact with skin or eyes.  To check each cell you need to be able to get to the electrolyte, meaning, are you able to remove the cell-cover caps. At this stage we are only doing a visual check of the electrolyte (the hydrometer test will come later) so going through the cells one-by-one check the electrolyte levels and record whether they are High, OK or Low.

Once you have done this you can move onto doing a Battery open circuit voltage (OVC) test. To do an OVC test you need your voltmeter, set on 20V, attach your Positive probe to the positive terminal of the battery and Negative probe to the negative terminal of the battery and wait for the reading, hopefully it should fall between 12.4v and 12.6v which converts into between 50% and 100% charge. Anything less and the battery is too undercharged to continue. Though to continue you can start the car to charge the battery, keeping your probes on the battery watch as the voltage comes up to at least 12.6v, if the voltage goes above 12.6v this is called surface charge, which you can get rid of by turning the headlights on for a minute or so or until the voltage hits the 12.6v mark.  

The third test you do is testing the battery electrolyte specific gravity this is where you use your hydrometer. When doing the hydrometer test, you need to remove the cell caps like you did with the visual electrolyte test. Again, you can only do one cell at a time, because you can only check one cell at a time with the hydrometer. So, removing the first cap carefully, by unscrewing it with your fingers (place the cap somewhere nearby as not to lose it) squeeze the top bobbly bit of your hydrometer which expresses all the air out of it and place into the cell, then let go of the top and the hydrometer should suck up all the liquid in the cell. On the side of the hydrometer there is a scale which gives you the specific gravity of the electrolyte. At the same time as reading the specific gravity you must also check the colour of the fluid, it should be clear; if it is murky it means that the plates are disintegrating. The level you are looking for in your electrolyte is around the 1280-1270 mark, this means that the battery has a high electrolyte level. After recording all 6 cells results you need to figure out the specific gravity variation of the battery, to do this you just minus the highest result from the lowest result for example if cell #1 had the lowest reading of 1240 and cell #5 had a reading of 1270 your specific gravity variation of the battery would be 30. The allowable specific gravity variation specification of a battery should be between 25 and 50.

The last test to do is a High rate discharge test or a Load test. Before starting this test you have to determine what load current you are going to apply, which is figured out by halving the batteries CCAs so on a battery with a total CCA of 310amps you would apply a load of 155amps. A voltage has to be held throughout the test, this voltage must be above 9.5v and not over 12.6v, the load must be held for 15seconds if it is not held for 15sec then the test fails. also before using the load tester make sure the load control is off, to do this you just have to turn the centre knob till the needle hits zero. When connecting the load tester to the battery you connect the positive lead to the positive terminal of the battery first, then connect the negative lead to the negative terminal of the battery, apply the specified load (in this example 155amps) by turning the load control knob, wait for the specified time (15secs) and take voltage held and load current readings. When the load tester beeps after the 15secs, immediately turn off the load tester by turning the knob till the needle hits zero, then disconnect the load testers leads in the reverse order.