Excessive Battery Discharge Rate

Overview

This procedure helps you measure the battery discharge rate on your Porsche 944 (16v engine) and identify why the battery might be draining too quickly when the car is off. A healthy battery should lose power slowly, but if something in the car is drawing too much current, it can leave you with a dead battery. This guide will walk you through checking the discharge rate and finding the culprit if it’s too high.

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Tools Required

• Digital Multimeter
• Test Leads (for the multimeter)
• Pen and paper (to record measurements)

Parts Required

• Battery (BCI Group 41 size, typically 50-70 amp-hours) – 944 611 041 00

Step-by-Step Procedure

Step 1: Prepare to Measure the Discharge Rate

1. Turn off the ignition and remove the key from your Porsche 944.
2. Locate the battery in the engine compartment (front of the car, under the hood).
3. Disconnect the positive battery lead from the battery terminal.
4. Connect the digital multimeter between the positive battery lead and the positive battery terminal using the test leads.
5. Set the multimeter to the ammeter function (current measurement) and turn it on.

Step 2: Check the Discharge Rate

6. Read the current draw on the multimeter. For the Porsche 944, it should be less than 65 mA (0.065 A).
7. If the reading is 65 mA or lower, your battery discharge rate is normal, and no further action is needed.
8. If the reading is higher than 65 mA, proceed to the next step to find the cause.

Step 3: Identify the Source of High Discharge

9. Locate the fuse box in the driver’s side footwell of the 944.
10. Remove one fuse at a time, checking the multimeter reading after each removal.
11. Write down how much the current draw decreases when each fuse is removed.
12. Reinstall the fuse before moving to the next one, repeating this process for all fuses.
13. Next, locate the relay panel (behind the fuse box or under the hood, depending on your 944’s setup).
14. Remove one relay at a time, noting the decrease in current draw on the multimeter for each.
15. Reinstall each relay after testing, continuing until all relays are checked.

Step 4: Pinpoint the Problem Component

16. Review your notes and identify the fuses or relays that caused a significant drop in current draw (e.g., more than a few mA).
17. Use the 944’s factory wiring diagrams to determine which components are connected to those fuses or relays.
18. Disconnect each component in those circuits one by one (e.g., interior lights, radio, or clock).
19. Check the multimeter after disconnecting each component. When the current draw drops significantly, you’ve found the source of the high discharge.
20. Repair or replace the faulty component as needed to resolve the excessive battery drain.

Post Procedure Checklist

• Ensure the multimeter reading is below 65 mA with all fuses and relays reinstalled.
• Check that the positive battery lead is securely reconnected to the terminal.
• Start the car to confirm the battery can crank the engine (minimum 10.5 VDC).
• Verify no warning lights or electrical issues appear on the dashboard.

Sources

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