Battery Test

Test the 12V battery condition, state of charge, and cranking/charging system performance using a digital battery tester to verify battery health and electrical system functionality.

Warnings

Tools required

Preparation

1. Ensure vehicle has been stationary with all electrical loads off for at least 1 hour for accurate resting voltage measurement
2. Open trunk and locate battery access panel on right side of trunk floor
3. Remove battery access cover (typically secured with quick-release fasteners or lift-up panel)
4. Verify battery tester is calibrated and set for AGM battery type
5. Note battery specifications: typically 12V 90-95Ah AGM type

Procedure

1. 1

   Visual Battery Inspection
   Inspect battery case for cracks, bulging, or leakage. Check battery manufacturing date code (typically stamped on top or side of case). AGM batteries typically have 4-6 year lifespan. Inspect battery hold-down bracket for security and corrosion. Check surrounding area for signs of acid damage or corrosion on body panels.
2. 2

   Inspect Terminal Condition
   Examine both positive and negative terminals for corrosion, looseness, or damage. Check terminal bolt tightness by hand (do not loosen if secure). Inspect cable ends for fraying, corrosion, or heat damage. Note any white/green corrosion buildup that may affect conductivity.
3. 3

   Measure Resting Voltage
   Using digital multimeter or battery tester, measure voltage across battery terminals with all loads off and ignition off. Reading should be 12.6-12.8V for fully charged AGM battery. 12.4V indicates ~75% charge, 12.2V indicates ~50% charge, below 12.0V indicates discharged or failing battery. Record voltage reading.
4. 4

   Perform Load Test
   Connect digital battery tester clamps to battery terminals (red to positive, black to negative). Enter battery specifications into tester (12V AGM type; enter the CCA/Ah rating printed on the battery label or per Aston Martin service data — verify the exact CCA before testing). Initiate load test per tester instructions. Tester will apply load equivalent to half the CCA rating for 15 seconds. Battery should maintain minimum 9.6V under load at 70°F (21°C), or 9.1V at 32°F (0°C). Record load test voltage. Note: Enter battery specifications into tester (12V AGM type). Use the CCA rating printed on the battery label rather than an assumed value, as entering an incorrect CCA will skew the tester's pass/fail judgment. Note: Enter battery specifications into tester (12V AGM type, CCA rating per battery label; verify exact CCA/Ah rating stamped on the installed battery against Aston Martin service data before testing).
5. 5

   Test Cranking System
   With battery tester still connected, have assistant turn ignition to start position and crank engine for 3-5 seconds (do not start engine). Tester will measure cranking voltage and current draw. Cranking voltage should remain above 9.6V during cranking. Observe cranking current draw on the tester. Compare the measured value against OEM service data; abnormally high current draw relative to specification indicates a starter or engine mechanical issue. Cranking voltage remaining above 9.6V is the primary health indicator. Note: Compare the measured cranking current draw against Aston Martin factory specification and battery tester guidance. Significantly excessive or prolonged high current draw may indicate a starter or engine mechanical issue. Significantly excessive or prolonged high current draw may indicate a starter or engine mechanical issue.
6. 6

   Test Charging System
   Start engine and allow to idle. With battery tester connected, measure charging voltage at battery terminals. Should read 13.8-14.4V at idle with no loads. Turn on headlights, HVAC blower on high, and rear defroster. Voltage should remain above 13.5V with loads applied. Rev engine to 2000 RPM; voltage should stabilize at 14.0-14.4V. Lower readings indicate alternator issue; higher readings (above 14.8V) indicate voltage regulator problem.
7. 7

   Check Ripple Voltage
   With engine running and battery tester in AC voltage mode (if equipped), measure AC ripple voltage across battery terminals. Ripple should be less than 0.5V AC. Excessive ripple (above 0.5V) indicates failing alternator diodes. Modern digital testers may display ripple as percentage; should be less than 10% of DC voltage.
8. 8

   Clean Terminals If Required
   If corrosion was noted during inspection and battery passed testing, shut off engine. Clean terminals using battery terminal brush on both terminal posts and cable clamps. Remove minimal corrosion without loosening terminals if possible. If terminals must be removed for heavy corrosion: disconnect negative first, then positive. Clean thoroughly. Reinstall positive first, then negative, torquing to the Aston Martin-specified value (verify in DB9 workshop manual; battery terminal clamps are typically in the 5-8 Nm range).
   Torque spec

   Battery Terminal Bolts6 Nm (4 lb-ft)
9. 9

   Document Test Results
   Record all test values: resting voltage, load test voltage, cranking voltage and amperage, charging voltage (idle and loaded), and ripple voltage. Compare results against specifications. Battery passes if: resting voltage above 12.4V, load test above 9.6V, holds above 9.6V during cranking, charges at 13.8-14.4V, ripple below 0.5V AC. Battery requires charging if voltage low but passes load test. Battery requires replacement if fails load test or voltage drops excessively under load.

Reassembly

1. If terminals were removed, ensure positive terminal is connected first, then negative, and torqued to 6.0 Nm
2. Reinstall battery access cover in trunk, ensuring all fasteners are secure
3. If battery was disconnected, reprogram power windows (cycle each window fully down then fully up while holding switch for 2 seconds in each position)
4. Verify clock, radio presets, and seat memory positions are retained or reprogram as needed

Verification

• Confirm all test values are within specification ranges and documented
• If battery was disconnected and reconnected, verify no warning lights on instrument cluster related to electrical system
• Test engine starting to confirm normal cranking speed and immediate start
• Check operation of all major electrical accessories (lights, windows, HVAC, audio system) to verify proper system voltage
• If battery charging issues were found, recommend alternator testing or replacement as separate repair

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