Water in the battery in a BMW 3 E90 – what is the cause?

BMW driver question

Today I noticed water in the battery compartment, it was never there until now, even when I replaced the battery with a new one, it was always dry. I am wondering how it got there. I checked everything:

• sides dry,
• the vent grille dry,
• lamps dry,
• fuel filler also.

The plugs under the battery are fastened so no water could get in there either. I have a new AGM Varty battery. Do you have any advice on how I had water in the battery compartment?

The problem was on a BMW E90 318, but it may also occur on other models.

BM Cars service response

The most common reason for water leaking into the trunk on the E90 is leaks caused by inaccurate sheetmetal repair in the rear body panels. An inaccurately glued rear window, a clogged tailgate drain, a bent tailgate gasket, or even a damaged rear door seal. These items can cause water to enter the trunk.

To find the specific cause, it is necessary to uncover the trunk upholstery elements and see if moisture has appeared on the side elements at the rear of the body. Then we can determine the exact path of water ingress. There is also a vent on the side of the rear body, which provides ventilation in the battery compartment.

Its absence or damage can also cause water to enter. There should be drain valves at the bottom of the battery compartment, which, when fully operational, should drain the accumulated water out of the vehicle.

A visual inspection of the vehicle is necessary for an accurate diagnosis.

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