Battery Tray Leaks and Repairs

Introduction

A leaking battery tray can cause serious electrical damage. On 944s with the DME located in the passenger footwell, water dripping from the battery tray runs onto the DME wiring harness and into the DME case. On turbocharged cars, the KLR unit can be affected as well.

Leaking battery trays typically develop when the battery tray drain becomes clogged and water stands in the tray for extended periods. Damage also occurs when the battery cover is missing — water washing over the unprotected battery carries acid off the battery terminals to the bottom of the tray.

Note: Remove the battery periodically, clean the tray thoroughly, and confirm the drain is free-flowing. Always ensure the battery cover is in place.

Selecting a Repair Method

Inspect the battery tray bottom to determine which repair is appropriate:

• Method 1 (sealer): Use when there are no visible holes or only very small holes in the tray bottom.
• Method 2 (metal replacement): Use when there are large holes or the tray bottom flexes easily under hand pressure, indicating general structural weakness.

Method 1 — Sealer Repair (Minor Damage)

1. For 944s with the DME in the passenger footwell, and for turbocharged cars with the KLR unit, remove these control units before starting repairs to prevent further damage.

2. Check the battery tray drain. Pour a cup of water into the tray and observe drainage. Clean the drain if clogged. Stuff rags around the underside of the tray to absorb any leakage during work.

3. Clean the entire battery tray with a mild soap and water solution. Rinse thoroughly. Remove all debris too large to flush through the drain.

4. Scrape the bottom of the tray with a metal scraper to remove loose paint. If rust discoloration is visible (easier to see on light-colored cars; difficult on dark paint), treat all affected areas with a rust converter. Apply the rust converter with a brush or spray following the manufacturer's instructions.

   Caution: Wear gloves, a mask, and eye protection when working with rust converter. Avoid skin contact.

5. After the rust converter is fully dry, coat the entire bottom of the battery tray with brushable seam sealer. For bare metal, prime the surface before applying the sealer. Apply brush strokes to resemble factory-applied seam sealer elsewhere in the engine compartment.

6. Once the seam sealer is dry, the battery tray may be painted to match the surrounding area. Seam sealer generally does not require priming before painting.

7. Reinstall the battery with its cover in place.

Method 2 — Metal Replacement (Severe Damage)

This method is required when the tray bottom is structurally compromised. It requires welding equipment and is beyond the capability of most home workshops without proper tools.

1. Determine the extent of the damaged area. Mark the boundary with a permanent marker or scratch awl. Remove the affected area using a cut-off tool, cutting torch, or plasma cutter.
2. Create a paper template by holding paper against the underside of the tray and tracing the cut-out area.
3. Transfer the template outline to replacement metal plate. Galvanized or stainless steel is preferred for corrosion resistance, though suitability depends on available welding equipment.
4. Cut out the new bottom and tack-weld it in place to prevent movement during final welding. Grind the welds smooth on the tray-side surface.
5. Coat the entire bottom of the battery tray with brushable seam sealer. Prime bare metal before applying sealer if desired.
6. Paint the repaired area to match the surrounding surface once the seam sealer is dry.
7. Reinstall the battery with its cover in place. Periodically remove the battery to clean the tray and verify the drain is clear.