Siren backup battery replacement.

[Autophilia]

Looks like I spoke too soon about my new A2 all working correctly, the alarm started sounding last night and after plugging it in to diagnostics and having a search on here it looked like it might be something to do with the backup battery in the siren.

A replacement unit is around £80 but If anyone wants to save a few quid and tackle this themselves take a look at the following.

The siren is located below the rear right tail light and requires some of the trim to be removed to access it, it's secured to a metal bracket with an m8 nut (13mm spanner)

You will need a sharp knife or scalpel, I used a small Stanley box cutter with the blade set out about 5mm

Next slide the knife all the way around the join in the casing, being careful not to cut any deeper than about 5mm, the plastic is soft and easy to cut with a decent blade.

Once you have cut all the way around, the case should open up.

Unclip the circuit board from the casing which exposes the battery (the green shrink-wrapped part) the spec is varta 2x3.6v 140mAh 2x3/V 150 H NiMH

As you can see the battery has leaked and is covered in crystallised electrolyte, the battery is reading about 0.1v so it's pretty dead.

It is possible that if the battery leaks more severely, that the electrolyte may damage the circuit board beyond repair but this one should just be a simple desolder and swap job.

Consensus seems to be that these batteries last about 10 years if you are lucky and according to the manufacture date this is the original that came with the car

I'll be ordering a new battery today and will update this thread with my progress.

 

[Autophilia]

It seems like it's not possible to get the vertical mounted double version but two of these will do the same job and are the same spec.

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/391113370772

I'll just add a couple of legs with some 20awg tcw to the tabs and they should be good to go, also have the benefit of knowing the batteries will be new and not something that could have been sat on the shelf in Audi's stores for years.

 

[Alan_uk]

I didn't know the alarm had a battery backup for itself so I thought for a moment that you may have mistaken it for a tracker but then I saw the Audi logo on the unit. I bet the tracker battery also has a life of about 10 years. With A2s getting scarce maybe that should be attended to as well (for those that have it installed). I guess it's a lithium or Ni Mh battery.

Autophilia, thanks for showing how easy this is - only 15 posts and you've have delivered a How To - excellent

 

[Evripidis]

I've done this three time so far for other makes but the manufacturer was common bosch on all three cases. They usually put out a warning when you turn the ignition on, e.g., 4 beeps or something similar. You should do this quick enough before the acid leaks and eats out the tracks on the pcb. In some versions there are tacks and through-holes for mounting batteries with various footprints. You cannot get those particular varta ones (with that footprint) for the general public. Best get them from farnell or cpc to make sure you get shelf-life stock.