Battery Testing

We were in pairs and had been assigned a battery for each pair. We were told and shown how to test the battery and had to work our way through the practical booklet we were given.

The battery Thomas and I were assigned was a Lucas conventional type battery with a 410 CCA rating. The battery number of which was 46G.

The first thing to do when testing any battery is to carry out visual checks. This consists of, battery terminals, surface, possible swelling of the battery etc. From this check it seemed as if the battery termials were clean and tight, there was no swelling of the battery evident. However, there was minor fluid apparent on the surface of the battery around the cells which could indicate leakage. Recommended further inspection.
We then had to remove the cell covers to check the electrolyte levels of each cell. Apparently if they are at the appropriate level, you will barely be able to see the cells at first glance as they will be covered by the electrolyte, however the level must not be too high. All our electrolyte levels appeared to be okay.

We then had to perform a battery open circuit voltage test. In this test it is important that surface charge is removed as it can give false readings. This can be achieved by turning on the headlights for approx 1-2 mins. When they are turned off the meter reading will drop and then build itself back up, where it stops is the reading needed. (The meter needs to be set to 20 DC volts) The result of this was 12.7v, which meant the state of charge on our battery was 100%. The battery must be over 50% charged before any other testing could be performed which meant ours was fine as it was over 12.4v. If it is lower than 50%, it must be charger slowly so as not to over exert itself.

As our battery was sufficient to continue testing we then began to test the specific gravity of the electrolyte. When this test is performed it is important that whoever is doing this test is wearing safety glasses and gloves as the electrolyte is an acid. Each cell needs to be tested individually with a hydrometer. This creates a vacuum which pulls the electrolyte into the hydrometer and makes the float float. First the fluid needs to be checked, if it is clear or murky. Then the reading, the variations of each of these cells should be no more than 50. In this regard our battery failed as our readings were: Cell 1: 1305; Cell 2: 1295; Cell 3: 1300; Cell 4: 1300; Cell 5: 1295; Cell 6: 1250. The specific gravity variation of this battery was 55.

We then carried out a high rate discharge test, using a load tester. The positive clip to be attached to the positive terminal and the negative to the earth terminal. This gave the load tester power. We then had to dial the amp on the load tester to half of the CCA rating which in this case was 205A. As it reaches the desired voltage, we must watch the voltage meter. The load should be held at 9.5v or over. Our battery held at 10.1v which means it was capable of holding its necessary load and is working.

When the engine is off, there are often things in a vehicle that can draw power from the battery. These at any given time should not be above 0.03Mv. If it is any more than this it will cause the battery to die very quickly. This is tested by adding an ammeter to the circuit as one of the components. (Series). Negative to negative terminal, positive to negative wire now unattached. The result of this test was 0 as we were working on engines off car, therefore there was no radio memory or anything to draw from the battery.

Report:

I recommend the battery terminals be cleaned as when the connection was removed for the draw test there was minor corrosion. This to be cleaned with hot water and baking soda until gone and then sealed with grease or petroleum jelly.
If the battery needed charging it should be done with a battery charger on slow charge.
If the amp draw were too high on the battery, the problem would be easily tracked down by keeping the circuit avaliable but removing possible draws until the amp drops. This would show what is drawing too much current while the engine is off.

When testing with a digital meter, it will simply tell you if your battery is pass or fail. The meter needs to be set to SAE and the CCA rating set. To test, the test button should be pressed and the screen will show a pass or fail. Our meter told us our battery failed which means that the battery needs to be replaced. Then press test button again to get O.C.V which was said to be 12.91v. From these results i would recommend cleaning the battery terminals and retesting in case corrosion caused false results. If it fails again, dispose of the battery.