Battery Checks

Overview

This procedure helps you inspect and test the battery in your Porsche 944 (16v engine variants) to determine its condition. A healthy battery is crucial for reliable starting and electrical performance, especially in a classic car like the 944. Start with a visual inspection, then move to condition testing if needed.

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Tools Required

• Wire brush
• Digital multimeter (with 0.5% accuracy or better)
• Needle-nose vise grips (for jump-starting or charging)
• 13mm wrench (for battery clamp bolts)

Parts Required

• Petroleum jelly (for corrosion protection)
• Felt rings for battery posts 944 611 999 00 (optional, for corrosion reduction)
• Battery cover 944 611 023 00 (to protect the tray and minimize corrosion)

Step-by-Step Procedure

Step 1: Perform Visual Battery Inspection

1. Look closely at the battery case for any cracks. If you see cracks, replace the battery, as this indicates damage.
2. Check the battery terminals for corrosion, which looks like white or rust-colored buildup on the posts or connectors.
3. If corrosion is present, use a 13mm wrench to loosen and disconnect the battery clamps. Clean the posts and clamps with a wire brush until they’re shiny.
4. Reconnect the terminal leads by tightening the clamps to 10 Nm (7 ft-lbs) with a 13mm wrench.
5. Apply a thin layer of petroleum jelly to the posts and clamps to reduce future corrosion. Optionally, install felt rings 944 611 999 00 around the posts.
6. Ensure the battery cover 944 611 023 00 is in place to protect the tray and minimize corrosion, a common issue in the 944.
7. Inspect the battery case for bulges. If you see any, the battery is failing and should be replaced.

Step 2: Test Battery Condition

8. Disconnect the positive battery lead using a 13mm wrench to isolate the battery.
9. Set your digital multimeter to DC voltage and connect it across the battery terminals (positive to positive, negative to negative).
10. Record the no-load voltage and compare it to this:

12.75 VDC: 100% charged

112.45 VDC: 75% charged

112.25 VDC: 50% charged

112.05 VDC: 25% charged

111.85 VDC: 5% charged

11. If the ambient temperature is below 21°C (70°F), adjust the reading: add 0.021 volts for every 1°C (1.8°F) below 21°C. For example, at 15°C (59°F), add 0.126 volts (6°C x 0.021).
12. Reconnect the positive lead and tighten to 10 Nm (7 ft-lbs) with a 13mm wrench.
13. If you can’t test at a professional auto parts store and the battery is sealed (common on 944 models), skip specific gravity testing, as it’s not possible.

Step 3: Evaluate Battery Replacement

14. Charge the battery for 6-8 hours at 13.8 to 14.6 VDC using an automatic constant voltage charger (see Step 4 for charging tips).
15. After charging, retest the no-load voltage as in Step 2. Replace the battery if:

Voltage is 0 VDC (indicates an open cell).

Voltage is 10.0–10.6 VDC (indicates a shorted cell).

Voltage won’t hold at least 12.45 VDC (won’t hold a sufficient charge).

Step 4: Charge the Battery (If Needed)

16. Use an automatic constant voltage charger set to 13.8–14.6 VDC.
17. Attach the positive charger lead to the battery positive terminal using needle-nose vise grips to avoid touching the windshield frame, a tight spot on the 944 S2.
18. Connect the negative lead to a ground point away from the battery (e.g., an engine bolt).
19. Charge for 6-8 hours. Avoid charging below 13.8 VDC or above 14.6 VDC to prevent shortening battery life.

Step 5: Jump-Start the Battery (If Needed)

20. If the battery is too weak to start the car, use jumper cables with another vehicle or a charger (no BOOST feature—see note below).
21. Connect in this order:

a) Dead battery positive (use needle-nose vise grips on the terminal).

b) Good battery positive.

c) Dead battery negative (to a ground point, not the terminal).

d) Good battery negative (to a ground point).

22. Start the car, then disconnect in reverse order.

Important: Never use a charger’s BOOST feature—it can damage the DME computer on the 944.

Post Procedure Checklist

• Ensure all connections are tight (10 Nm / 7 ft-lbs) and free of corrosion.
• Check that the interior lights turn on brightly, indicating sufficient charge.
• Verify the battery cover 944 611 023 00 is secure.
• Test-start the engine to confirm the battery holds a charge.

Sources

• Clark’s Garage
• Pelican Parts
• Porsche 944 Workshop Manual, Volume 1
• Youtube