X5 – Corrosion Around The Battery Tray

Like many BMWs of its era, the E53 X5 has its battery mounted in the centre of the boot floor. It sits in a large, thick plastic tub, and the floor pan has a large rectangular cut-out for this plastic tub. It seems common for the floor pan to corrode around the edges of this cut-out, so I ripped it apart to find out how my X5 was doing.

I discovered a little rust. Nothing too bad, but certainly worth remedial action, and enough to compel me to get underneath and search for more. When it comes to rust, I really like to address it fast. All the time there’s just a bit of surface corrosion, I can deal with it myself. If the metal is allowed to weaken, it becomes much more of a PITA.

So here’s what I found when I’d removed the battery and its tray.

I have a standard protocol with incidents like this: wire brush (manual / drill attachment), sandpaper by hand, clean, white spirit, rust treatment, clean, white spirit, direct-to-rust anti-rust sealant paint. So that’s what I did. I also chose to treat the whole perimeter of the cutout, both from on top and underneath.

The black Hammerite paint can be seen when the plastic tray is refitted, but I’m okay with that. As more and more layers of X5 kit are loaded in, the whole thing disappears from view. First the battery, audio and centre screen graphics unit go in.

Those electrical items are then covered.

Then the air suspension pump goes on top.

Then the spare wheel and jack.

Spare wheel cover.

Boot floor.

It is probably worth mentioning that the X5 has a UK Custom Covers erm, cover installed. I find these things vital to prevent dog hair and general mud finding its way into vehicle upholstery. I’ve got covers in both the 330d and 335d, too.

While I was under the car I brushed off the underside of the floor pan and the rear sub-frame, and treated and painted those too. I now realise I didn’t photograph those specifically at the time, but there is evidence forthcoming in posts on other topics that I hope to release soon.

I do have this shot taken under the car prior to the work:

And this taken after the work, in which it is possible to see that the rear sub-frame has been treated. More on that shiny new bolt in another post!