Battery Testing
Battery Testing
There are four steps to follow in testing an automotive battery:
- Inspection
- Removal of Surface Charge
- State-of-Charge Test
- Load Test
Tools Needed
To test a battery following tools are needed:
- DVOM Digital Volt Ohm Meter
- Battery Load Tester (i.e. Snap On VAT 60)
- DISplus or MoDic
- Battery Draw Test Special Tool PN 61 2 300
- Closed Circuit Measurement Adapter PN 90 88 6 612 310
- Temperature Compensating Hydrometer
Inspection
Visual inspection is important for the detection of obvious problems:
- Loose Generator Belt
- Low Electrolyte Level
- Corroded Cable or Terminal Clamps
- Loose Hold-Down Camps or Cable Terminals
- Damaged Battery Case
NOTE: The proper electrolyte level is just covering the plates, not all the way to the top of the battery inspection holes.
Removal of Surface Charge
If the battery has just been recharged, or the car has been driven, eliminate any surface charge by one of the following methods:
- Allow the battery to sit for 2-3 hours.
- Turn the headlights on high beam for 5 minutes and wait 5 minutes after turning off.
- With battery load tester, apply a load of 1/2 the battery's CCA for 15 seconds, then wait 5 minutes.
State-of-Charge Test
Use the table to determine the battery's State-of-Charge.
Pay special attention if the DVOM measurement of OCV is equal to:
- 0 volts -Indicate an open cell.
- 10.45-10.65 volts -Indicates a shorted cell.
For non-sealed batteries, check both specific gravity (SG) in each cell with a temperature compensated hydrometer and battery OCV without the engine running.
For sealed batteries, measuring the battery's CCV (without the engine running) with an accurate DVOM is the only way to determine the state-of-charge.
Batteries with a built-in hydrometer measure the state-of-charge in one cell only If the indicator is clear or light yellow, the battery has a low electrolyte level and should be refilled before proceeding or replaced.
A state-of-charge reading BELOW 75% using SC, voltage measurement or dark indicator in batteries with built-in hydrometers, indicates the battery must be recharged before proceeding.
Replace the battery if one or more the the following conditions are met:
- More than 0.050 difference in the specific gravity readings between the highest and lowest cell (There is a weak or dead cell).
- The battery will not recharge to 75% or greater state-of-charge or the built in hydrometer does not indicate good (green indicates 65% or better).
- DVOM reading indicates 0 volts (Open cell).
- DVOM reading indicates 10.45-10.65 volts (Shorted cell).
Load Test
A battery which has a state-of-charge of 75% or greater or has a "good" built-in hydrometer indication may be load tested.
With a battery load tester properly installed, load the battery for 15 seconds to one of the following:
- One-half (1/2) the CCA (Cold Cranking Amps).
- Three (3) times the AH Rating (Amp Hour Rating).
The voltage on a good battery will NOT drop below 9.7 volts during the battery load test. After the load is removed, wait 5 minutes, the battery should bounce back to 50% or greater state-of-charge. If a battery drops below 9.7 volts during the load test, does not bounce back or fails to start the engine, the battery should be replaced. Batteries which pass this test should be recharged to restore peak performance.
Load Test Conditions
Tests assume electrolyte temperature of 80°F, 26.7°C.
If the electrolyte temperature is above 80°F add .1 volt for every 10 degrees up to 100°.
If the temperature is below 80°F subtract. 1 volt for every 10 degrees to 40°.