Batteries come in many sizes and power ratings, so always check the rating of the battery you are servicing. The objective of this procedure is to show you how to inspect and test a battery.
Part 1. Preparation and safety
- Inspect and test a battery.
Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:
- Work clothing – such as coveralls and steel-capped footwear
- Eye protection – such as safety glasses and face masks
- Ear protection – such as earmuffs and earplugs
- Hand protection - such as rubber gloves and barrier cream
- Respiratory equipment - such as face masks and valved respirators
If you are not certain what is appropriate or required, ask your supervisor.
- Make sure that the hood is secure with a hood stay rod.
- Always make sure that you wear the appropriate personal protection equipment before starting the job. Remember that batteries contain acid and it is very easy to hurt yourself even when the most exhaustive protection measures are taken.
- Always make sure that your work area/environment is as safe as you can make it. Do not use damaged, broken or worn out workshop equipment.
- Always follow any manufacturer's personal safety instructions to prevent damage to the vehicle you are working on.
- Make sure that you understand and observe all legislative and personal safety procedures when carrying out the following tasks. If you are unsure of what these are, ask your supervisor.
Points to note
- Batteries come in many sizes and power ratings, so always check the rating of the battery you are servicing. The rating provides a testing benchmark for battery performance.
- The hydrometer used to measure the specific gravity of the electrolyte must be handled carefully and safely.
- Store the hydrometer in a safe receptacle before and after use. Small amounts of electrolyte in the hydrometer can leak out and damage the vehicle paintwork.
- Do not remove electrolyte from one cell to another when testing; this will cause incorrect readings.
Part 2: Step-by-step instruction
- General condition checks
Switch on the ignition. The charge light on the dash should light up, and go out when you start the engine. This indicates that the alternator is charging the battery. Turn the engine off. Switch on the headlights of the vehicle, then start the engine and see if the lights brighten significantly. If they do, then this indicates that the alternator is charging the battery more than it is being drained by the lights. If you do not have someone else to start the engine for you, judge the brightness by shining the lights onto a reflective surface such as a wall. Check that the battery casing and the terminals are in good condition. This can generally be achieved just with a visual inspection, however, since the battery may be located in a position where you cannot see all of it, you may have to remove it to complete the inspection, after performing any other on-car tests.
- Check and adjust fluid level
A sealed or low-maintenance battery has no removable cell covers, so you cannot adjust or test the fluid levels inside However, some of these do have visual indicators that provide information on the status of the charge and condition of the battery cells. Each manufacturer provides details of these visual indicators so refer to these when undertaking an inspection. If the battery is not a sealed unit, it will have removable caps or bars on top. Remove them, and look inside to check the level of the battery fluid, which is called the electrolyte. If the level is below the tops of the plates and their separators inside add distilled water or water with a low mineral content until it just covers them. Be careful not to over-fill the cells as they could “boil” over when charging.
- Conduct specific gravity test
Test the specific gravity of each of the cells by using a hydrometer designed for battery testing. Draw some of the electrolyte into the tester and look at the float inside it. A scale indicates the relative charge state of the battery by measuring how high the float sits in relation to the fluid level. A very low overall reading of 1150 or below indicates a low state of charge. A high overall reading of about 1300 indicates a high state of charge. The reading from each cell should be the same. If one or two cells are very different from the rest that indicates there is something wrong with the battery.
- Conduct voltage test with DVOM
Select the Volts DC position on your DVOM and attach the probes to the battery terminals (red to positive and black to negative). With all vehicle accessories switched off and the battery at 70 degrees Fahrenheit or 21 degrees Celsius, the voltage reading should be 12.6 volts if the battery is fully charged. This will be slightly lower at cooler temperatures.
- Conduct load test
Measure the continuous load capability of the battery with a load tester. Refer to the manual of the particular tester for its operating instructions. A load tester induces a high rate of discharge in the battery, like the load created by a cranking starter motor. A battery is rated in ampere hours, which means that it can supply a certain number of amperes for a specified length of time under continuous load. Another measurement used is International Standard Cold Cranking Amps. Check the specifications for the battery you are testing. If it can meet these specifications under a load test then it is in good condition. There are different makes and types of load testers. Always use the equipment manufacturers recommended testing procedure.