Battery Test

This procedure tests the battery condition and charging system performance on a 2007 Ram 3500 with 5.9L Cummins diesel engine to verify adequate cranking power and electrical system health.

Warnings

Tools required

Preparation

1. Park vehicle on level surface and apply parking brake
2. Turn off all electrical accessories including headlights, radio, and climate control
3. Turn ignition key to OFF position and remove key
4. Allow vehicle to sit with engine off for at least 2 hours for accurate resting voltage test (ideally overnight)
5. Open hood and locate battery or batteries (dual battery setup common on Cummins diesel models)
6. Inspect battery case for cracks, damage, or swelling

Procedure

1. 1

   Visual battery inspection
   Inspect both batteries (if dual battery system) for physical damage, corrosion, and proper mounting. Check that batteries are securely held in place by hold-down brackets. Examine battery terminals for excessive corrosion, loose connections, or fraying cables. Look for signs of electrolyte leakage around posts or case seams. Note the battery manufacture date code - batteries older than 4-5 years may require replacement regardless of test results.
2. 2

   Clean battery terminals if needed
   If corrosion is present on battery terminals or cable ends, disconnect negative cable first, then positive cable. Clean terminals and cable ends with wire brush or battery terminal cleaner until bright metal is visible. Reconnect positive cable first, then negative cable. Ensure connections are tight and secure. This ensures accurate test results.
3. 3

   Measure resting battery voltage
   Set digital multimeter to DC voltage (20V scale). Connect red probe to positive battery terminal and black probe to negative terminal. A fully charged 12V battery should read 12.6-12.8V. Between 12.4-12.6V indicates 75% charge. Below 12.4V indicates battery needs charging before further testing. For dual battery systems, test each battery individually. Record voltage readings for both batteries.
4. 4

   Perform battery load test
   Connect battery load tester to battery terminals following manufacturer instructions. Apply load equal to half of the battery's CCA (Cold Cranking Amps) rating for 15 seconds. The 5.9L Cummins uses dual batteries; each is typically rated around 600-750 CCA (combined ~1200-1500 CCA). Verify the exact CCA rating stamped on the batteries and the requirement in the service manual. During load test, voltage should not drop below 9.6V at 70°F (higher minimum at warmer temperatures, adjust per load tester specifications). If voltage drops below threshold, battery has failed and requires replacement. Repeat test for second battery if equipped with dual battery system.
5. 5

   Test cranking voltage
   Reconnect multimeter to battery terminals. Disable fuel injection to prevent the engine from starting during cranking. On the 2003-2007 5.9L common-rail Cummins, fuel is controlled electronically by the ECM, so use a scan tool to command 'disable injectors / clear flood mode' or disconnect the fuel pump relay rather than any injection-pump solenoid. Have assistant crank engine for 3-4 seconds while observing voltage. Have assistant crank engine for 3-4 seconds while observing voltage. Voltage should not drop below 9.6V during cranking on the 5.9L Cummins diesel. Lower voltage indicates weak battery, poor connections, or starter draw issues. For dual battery systems, monitor voltage at both batteries during cranking.
6. 6

   Test charging system voltage
   Restore fuel injection (reconnect fuel pump relay and/or clear any injector-disable command via scan tool) if disabled. Start engine and allow to idle. Measure voltage at battery terminals with engine running. Voltage should read 13.8-14.4V at idle, indicating proper alternator charging. Increase engine speed to 1500-2000 RPM and verify voltage remains in range. Turn on high electrical loads (headlights, heater blower on high, rear defroster) and verify voltage stays above 13.5V. For dual battery systems, both batteries should show similar charging voltage.
7. 7

   Check for voltage drop in cables
   With engine running at idle, measure voltage drop across battery cables. Connect multimeter positive probe to battery positive post and negative probe to alternator B+ terminal. Voltage drop should not exceed 0.5V. Repeat test on negative side by connecting positive probe to battery negative post and negative probe to engine block ground. Excessive voltage drop indicates corroded connections or undersized cables requiring service.
8. 8

   Document test results
   Record all test measurements including resting voltage, load test results, cranking voltage, and charging system voltage. Compare results against specifications. For dual battery systems, both batteries should show similar performance. If one battery tests weak, both should typically be replaced together to ensure matched performance. Note any abnormal findings such as excessive voltage drop or charging system irregularities for further diagnosis.

Reassembly

1. Ensure all battery connections are tight and secure after testing
2. Apply dielectric grease or battery terminal protector to terminals to prevent future corrosion
3. Verify battery hold-down brackets are properly secured
4. Clear any diagnostic trouble codes that may have set from disabling fuel system during testing

Verification

• Confirm battery resting voltage is 12.6V or higher
• Verify battery maintains voltage above 9.6V during load test and cranking
• Confirm charging system produces 13.8-14.4V at idle and under load
• Ensure no excessive voltage drop in battery cables (less than 0.5V)
• For dual battery systems, verify both batteries show similar test results
• Test start engine multiple times to confirm adequate cranking power for 5.9L Cummins diesel
• Verify all electrical accessories function properly after testing

Related trouble codes on this vehicle

Codes that commonly send this job to the bay — tap one for symptoms, causes, and diagnostic steps.

Chasing one of these codes and not sure which part is guilty? Ask a master mechanic about YOUR car →

More procedures for this vehicle