The first test of a battery is a visual inspection. There are certain things a technician should look for when inspecting a battery. Some things to look for include the quality of the connection from the battery to the cables.
Cracks or other leaks can cause acid spills. Missing battery hold down hardware can cause damage to the plates inside the battery from it being allowed to hop up and down from bumps in the road.
Dirt buildup on the top of the battery can actually cause a parasitic drain between the posts. Be sure to clean the top of the battery with battery cleaner. Missing factory heat shielding (insulators) will shorten the battery's life. As a guideline, every 15°F/8°C rise in temperature above 77°F/ 25°C will cut the battery life in half. A battery that might last for 10 years at 77°F/25°C will only be good for five years if operated at 95°F/33°C.
Likewise, the same battery might only withstand a little more than one year at a temperature of 107°F/42°C. Have you ever seen a battery located directly behind or very near a radiator? Be sure to clean and reinstall all battery heat shields when replacing a battery. True, some batteries may have case designs that help protect it, but even still, the factory shielding should be left in place. Check to make sure it is the right battery for the vehicle. Does it fit the tray? Does it interfere with hoses or wiring? Does the CCA rating at least meet the minimum CCA required as stated by the manufacturer of the vehicle?
One of the testing tools that can be used is a hydrometer. The problem however, is that it has become very impractical with today's batteries and vehicle designs. As a result, testing the specific gravity of the acid with a hydrometer is fast becoming a rarity in the real world of automotive repair.
At 80°F/26.7°C, if the specific gravity of the acid is 1.265 in each cell, then each cell is fully charged. At 1.225, it is 75%. At 1.190 it is 50%. At 1.55 it is 25%. Finally, if it is 1.120 then it is flat dead. Again, those readings are at 80°F/26.7°C, temperature effects this measurement, so you will have to calculate temperature changes at different temps. Add or subtract 4 points (.004) for every 10°F above or below 80°F/26.7°C.
Some batteries already have a built-in hydrometer. The green "eye" in some brands of batteries is type of a hydrometer. The problem with those however, is that they only test the one cell they are mounted into. It is very possible to have that one cell test "good," yet fail every other cell in the battery. In the real world of battery testing, load testing is the most popular.
Accurate load testing does have one down fall, the battery must be at least 75% charged before testing. First, check the unloaded voltage between the posts. Typically a fully charged automotive battery has an unloaded voltage reading of 12.6vdc. That is because each cell contributes an average of 2.1vdc, added up over 6 cells, is 12.6vdc. A battery is said to be 75% state of charge at 12.4 volts.
A completely discharged battery can still have a voltage reading as high as 11.9 volts. Readings slightly over 12.6, like up to 13.6 volts, may simply be a surface charge that has to be removed before testing. Extremely high voltage readings such as 16 volts, is an indication of a sulfated battery. A voltage reading that is exactly 2.1vdc low (10.5 volts) is the indication of an inactive cell.
Notice how the slightest voltage difference means so much about the condition of the battery. There is only a seven tenths of a volt difference between a fully charged battery, and one that may not even work the dome lights.
The accuracy of the DVOM, or preferably a designated battery tester, used must not be questionable, and should periodically be tested against a known voltage source.
After you have performed your no-load voltage test and have verified the battery is at full charge, it is time for the load test. First, if there is a surface charge, it will have to be removed. Giving the battery a 50-amp load for 10 seconds should remove the surface charge. The no-load voltage should return bounce back to somewhere between 12.4 volts and 12.6 volts. If it is too low, the battery must be recharged before testing. If recharging doesn't correct it, then replacement is in order. If it does pass, continue with the test.
Load the battery to 50% of the CCA rating for 15 seconds. Watch the voltage rating. At the end of the 15 seconds, record the voltage. If it fell below 9.6 volts at 70°F/26°C and above, the battery fails the test. For every 10°F/6°C drop below 70°F/21°C until 40°F/4°C is reached, subtract 0.1v from the 9.6 volt minimum. In other words, a battery that reads 9.3 volts at 70°F/26°C fails, but a battery that reads 9.3 volts at 40°F/4°C passes. Below 40°F/4°C, the amount to subtract is 0.2 from 9.3 volts for every 10°F/6°C drop until you reach 0°F/-17.8°C. Do not attempt load testing below that point, and never attempt to recharge a battery below 40°F/4°C, do to the possibility of the vents being blocked with ice. Obviously, if you are to load the battery to half of its CCA rating, a load tester capable of drawing up to 500 amps will be required as many batteries have a CCA rating of up to 1,000 amps.
Fixed load testers (the kind with the little toggle switch on the bottom) usually only have an amperage draw of 100 to 125 amps. Those may work fine on motorcycle or lawn tractor batteries, but for the average car battery, (many around 700 CCA) they fall short.
OK, let's say the battery passes the load test, is it OK to label it "good" yet? Not yet, there are still a couple of other things we need to look at. One, is the bounce back time. After the load test, and over the next 10 to 15 seconds, the battery should be bouncing back up to around 12.4v or over. If it takes too long, then replacement of the battery should be suggested. Likewise, if it bounces back too fast, the battery is likely sulfated and may require either a slow charge, or replacement.
Another thing to monitor is the amperage from the alternator. Assuming that the alternator is good at this point, start the engine and place an ammeter on the charge lead from the alternator. If the battery was at full charge before the startup, and the startup is the only thing that happened to the battery, monitor the amps from the alternator. One company suggests to replace the battery if the charging amps from the alternator into the battery are still over 30 amps after 30 seconds. That test may come in handy after replacement of an alternator, to help prevent repeat alternator failures.
Conductance testers are the newest battery testers on the market. The advantage to a conductance tester is that the battery doesn't need to be fully charged. In fact, it doesn't need to be charged at all. A conductance tester does not place a load on the battery. Instead, it sends an AC signal through the plates of the battery to map out the condition of the plates. That information allows the tester the even calculate the battery's CCA rating.
Proper Recharging
From time to time, you may get a battery that may require recharging. Maybe someone left a light on over night, or maybe the alternator failed and the battery is low. The actual charge time is going to depend on several things, like temperature, how low the battery is on charge, the rate of charge employed, the reserve capacity of the battery, type of charger used, and quality of connection made by the clamps the charger uses.
For the average size automotive battery, and use of a charging rate that doesn't risk damage to the battery, expect a proper charge time of 7 to 14 hours. Most customers aren't that patient, but that is the realistic charging time required. If the battery is not fully charged, by the charger, then the alternator is expected to do the job.
An alternator is not a battery charger, it is a battery maintainer. The alternator is already heavily taxed running all those electrical goodies the customer wanted, its not supposed to have to "fill up" the battery from "empty" as well. Make sure the battery is at least 40°F/4°C. Do not remove the vent caps. Use a low rate of charge, we all get busy, it is too easy to forget that battery over their "cooking" until we smell it.
It is a good idea to remove the battery from the car to reduce the chances of damage to the vehicle's electronics from voltage spikes. Also, to help protect the vehicle in case of a battery explosion. Some battery chargers have built in computer controlled devises to aid with the charging process.
They perform conductance testing of the battery and vary the charge rate to shorten the charge time without damaging the battery.
Use a proper charging adapter for side post batteries, a bolt doesn't count and can actually cause damage. The steel bolt gets hot and can distort the plastic case causing it to leak. After charging is complete, it is a good practice to unplug the charger before disconnecting it from the battery.
Proper Replacement
Every job has proper tools and procedures, battery replacement is no different. A side post terminal wrench should be used to prevent damage to the battery bolt. They are also insulated to prevent grounding out the battery.
A battery cable puller should be used to prevent damage to the cable clamp, and prevent damage to the battery should it need to be reinstalled. Not every battery has built in straps, so the battery should be handled with a battery carrier to protect the technicians hands (and feet if he looses his grip).
The torque values of the tapered top post clamp are 50 to 70 inch pounds, the side post style is 79 to 90 inch pounds, and the stud terminals used on marine batteries is 120 to 180 inch pounds. The top bar-style hold down bracket has a torque spec of 30 to 50 inch pounds, the bottom recess-type hold down is spec'd at 60 to 80 inch pounds and the bottom ledge style hold down is spec'd at 73 to 90 inch pounds. Now, I don't expect anyone to actually break out the torque wrench.
The cables should be inspected and either cleaned or replaced. Some of these cables are a part of several hundred-dollar engine-wiring harnesses.
The vehicle is designed the way the vehicle is designed. Total cable replacement is the best method of handling corrosion that has penetrated the copper wiring under the insulation, in my opinion. Some companies offer a cable end replacement that actually has about 7 or 8 inches of cable attached onto the clamping end. The cable is spliced onto the battery cable away from the battery.
These, at least, are better than the temporary clamp on ends that are only a cable end and nothing more, because at least you may be able to get away from the corroded end of the cable. Some shops will crimp and solder on several inches of replacement cable and a new terminal end. However you choose to handle this, remember that a new cable end is useless unless the cable is corrosion free. If corrosion is left, the connection point will likely have a higher resistance. That resistance may prevent proper battery cycling. Also, corrosion has a natural tendency to spread and will, over time, reverse any repair attempts previously made.