Battery Test

Perform a complete battery test to evaluate the condition, state of charge, and cranking power of the battery in a 1970 AMC Rebel Machine.

Warnings

Tools required

Parts

• Battery terminal cleaner spray (optional) × 1 — Use any automotive electrical cleaner

Preparation

1. Park vehicle on level ground and engage parking brake
2. Turn off engine and remove ignition key
3. Turn off all electrical accessories including lights, radio, and heater blower
4. Allow engine to sit for at least 1 hour if recently driven to get accurate resting voltage
5. Locate battery in engine compartment on passenger side near firewall
6. Ensure battery top is clean and dry for accurate testing

Procedure

1. 1

   Perform visual battery inspection
   Inspect battery case for cracks, bulging, or leakage. Check electrolyte level through case (if translucent) or filler caps. Examine battery terminals and cable ends for corrosion, looseness, or damage. Look for corroded or frayed cables. Note the battery date code if visible. A battery more than 4-5 years old may need replacement regardless of test results.
2. 2

   Check battery terminal connections
   Without disconnecting, attempt to twist battery terminals by hand. Terminals should be tight and immobile. If loose, tighten terminal clamp bolts with appropriate wrench. Clean any visible corrosion from terminals and cable ends using wire brush or battery terminal cleaner. Ensure good metal-to-metal contact for accurate testing.
3. 3

   Measure resting voltage
   Set digital multimeter to DC volts (20V scale). Connect red probe to positive battery post and black probe to negative post. Record voltage reading. A fully charged 12-volt battery should read 12.6-12.8 volts. 12.4 volts indicates 75% charge, 12.2 volts indicates 50% charge, and below 12.0 volts indicates a discharged battery. If below 12.4 volts, battery should be charged before load testing.
4. 4

   Check for surface charge
   If voltage reads above 12.8 volts, battery may have surface charge from recent charging or driving. Remove surface charge by turning on headlights for 30 seconds, then turn off and wait 2 minutes. Re-measure voltage. This provides accurate resting voltage for state of charge determination.
5. 5

   Perform battery load test
   Connect battery load tester according to manufacturer instructions, ensuring good contact with battery posts. The 390ci V8 with standard equipment requires approximately 300-350 cold cranking amps. Apply load at 1/2 the CCA rating stamped on battery for 15 seconds while monitoring voltage. Battery voltage should not drop below 9.6 volts at 70°F during load test. If voltage drops below 9.6 volts, battery has insufficient capacity and should be replaced.
6. 6

   Test voltage recovery
   After removing load, observe how quickly voltage recovers. Battery should return to at least 12.4 volts within 30 seconds. Slow recovery or failure to reach 12.4 volts indicates weak or sulfated battery that cannot hold charge properly.
7. 7

   Perform cranking voltage test
   Reconnect load tester or use multimeter connected to battery. Disable ignition system by disconnecting coil wire at distributor cap and grounding it to engine block. Have assistant crank engine for 5-10 seconds while monitoring voltage. Cranking voltage should remain above 9.6 volts. If voltage drops below this threshold, battery is weak or has excessive internal resistance.
   ⚠Ensure coil wire is properly grounded away from carburetor to prevent fire hazard during cranking.
8. 8

   Check charging system voltage
   Reconnect coil wire if disconnected. Start engine and let idle. Measure voltage across battery terminals with engine running at idle, then again at 1500-2000 RPM. Voltage should be 13.8-14.8 volts, indicating proper alternator function. If voltage is below 13.5 volts or above 15.0 volts, charging system has issues that may affect battery life and should be addressed separately.
9. 9

   Test for parasitic drain (if battery discharges when parked)
   Turn off engine and all accessories. Disconnect negative battery cable. Set multimeter to DC amps (10A scale initially). Connect multimeter in series between negative cable and negative battery post. Normal draw should be less than 50 milliamps (0.050A). Higher draw indicates parasitic drain requiring further diagnosis. The 1970 Rebel Machine has minimal electronics, so draw should be very low.
10. 10

    Document test results
    Record all voltage readings, load test results, and observations. Compare battery CCA rating (stamped on battery) with test results and engine requirements. Note battery age if determinable. Based on all test data, determine if battery passes (all tests within specification), needs charging (low voltage but passes load test), or requires replacement (failed load test, low CCA, or excessive age).

Reassembly

1. Ensure negative battery cable is securely reconnected and tightened if previously removed for testing
2. Apply thin coat of petroleum jelly or terminal protector spray to battery posts and cable ends to prevent corrosion
3. Ensure all tools and test equipment are removed from engine bay

Verification

• Battery voltage at rest should be at least 12.4 volts for a serviceable battery
• Load test voltage should remain above 9.6 volts under specified load
• Engine should crank strongly with voltage remaining above 9.6 volts
• Charging system should produce 13.8-14.8 volts with engine running
• No excessive parasitic drain present if battery discharges when parked
• All electrical systems function normally after testing

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