"Another issue can be with remote-mounted batteries, often found in vehicle trunks to save space under the hood. If techs test the battery using the underhood booster terminals, this may lead to falsely diagnosing a battery as bad. Additional resistance caused by the length of the cable can often result in inaccurate battery diagnosis. If a remote-mounted battery is tested and fails, techs should locate the battery and directly test it, to confirm if it’s an issue with the battery or if the issue is elsewhere."
"Testing failures in a vehicle must be confirmed after the battery is removed from the vehicle. Readings made while connected in the vehicle can be affected by poor connections, active loads, and effects from recent operation", added Knauer. The importance of connecting directly to the battery for accurate test results was echoed by nearly every expert I asked. I know I'll take a different approach from now on!
On to performance testing
I was first taught to use a carbon pile load tester to test the vehicle's battery. Later in my career, I was introduced to the handheld conductance testers that are popular (and required) by many OEMs. Today, personally, I prefer the use of a DSO (Digital Storage Oscilloscope) to test the battery. What do the experts have to say? Let's start with this great overview Knauer shared:
"LOAD TESTING: The gold standard for serviceability of engine starting batteries is a load test conducted according to the Battery Service Manual published by BCI (Battery Council International). A load of ½ the CCA rating is applied for 15 seconds. The voltage must not fall below a limit that depends on the core battery temperature at the start of the test. The battery must initially be at least 75% charged which correlates to a well-rested, open-circuit voltage of 12.4 or higher.
CONDUCTANCE TESTING: Conductance testers that correlate to BCI standard load test results are useful tools. They may provide a quick decision or they may say CHARGE AND RETEST. You may trade some accuracy for speed, but it is generally worth the time saved. The user must connect it properly, avoid putting in incorrect data to the tester, charge the battery properly before retesting when requested by the tester, and reconfirm failed results obtained in a vehicle after the vehicle connections are removed from the battery terminals and the terminals are cleaned. Proper connections to side or stud terminals REQUIRE that charging adapters be used properly.
|(Image courtesy of Clore Automotive) Conductance testing is one of two acceptable ways to performance test the battery. Just be sure to properly input the test parameters - battery rating, type, etc.|
DIAGNOSTIC FAST CHARGERS: These can be effective, but their potential to streamline the warranty process too much and not do more extensive testing must be weighed against the possibility of increased warranty and added replacement costs. Following recommended safety procedures (shielding, etc.) is a must when using these testers.
BATTERY SENSOR EQUIPPED VEHICLE: A battery sensor equipped vehicle continuously monitoring the battery should be able to make a much more informed decision than any quick test by a technician, but some level of secondary confirmation may be required for warranty situations on a case-by-case basis."
Exide's McLaughlin agrees, adding, "We (also) recommend the methods as outlined in the BCI Service Manual. The first is the carbon pile test. At 15 seconds if the battery is (less than) 9.7 volts, it should either be replaced or recharged and re-tested. Batteries greater than 9.7 volts can be returned to service. The second is a conductance test with one of the various meters available on the market. We recommend following the meter’s guidance on whether the battery is Good, Bad/Replace or Recharge and Retest. We do not advise making decisions solely on the estimated CCA rating output."
|(Image courtesy of Clore Automotive) Still an industry standard, the carbon pile load tester should be used to "load" the battery to 1/2 of its CCA rating for 15 seconds — then observe the OCV reading. It should remain above 9.7v.|
So I think what we've learned so far is that either testing method will provide us accurate results IF we insure that we are connecting our tools directly to the battery. If you take a quick test in the vehicle and it passes, you'll probably be ok but if the initial test is questionable, you'll need to remove the battery and test directly at the posts.