It is however possible to cut open the alarm and replace the 7.2v Mimh battery with a custom battery pack made of 6 aaa rechargeable battery cells.
To take out the alarm:
-Disconnect the car battery in the trunk,
– remove the front passenger side wheel
– drill out the 4 front rivets, and remove the 2 bolts holding the plastic wheel well.
– fold the plastic out of the way. The alarm is in the top right corner.
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– next step is to remove the flat bolt holding the alarm. I used a dremmel too to create a slot for a flat screwdriver. you will need a short screw driver.
– once the bolt is out, push the alarm up and out, to clear tab. Here is what it looks like once taken out.
The screw driver on the picture is pointing to the tab.
– after removing the connector you can take the alarm out.
– take out the alarm out it it’s metal bracket a cut it open a the junction of the two plastic part. I used a band saw for this.
Just make sure you don’t cut too deep or you will cut the plastic tabs that are holding the circuit board. The cut should be about 3mm deep.
– once open, remove the existing battery by breaking the plastic tab holding it.
– it is almost impossible to find the same battery, and removing it does require to break the plastic part holding it. Instead, I went to batteryplus store to a custom battery pack made of aaa Mimh cell, for about $28. Here is the replacement battery pack with the circuit board. I had the store reuse the original connector to built the battery pack.
– you have to trim all the plastic parts that was used to hold the original battery to make the bottom the box flat. It is a tight fit but it will work.
– I used a hot glue gun to glue the new battery pack to the bottom of the box. Try first to see where the battery can fit to let you close the box.
– I added one drop of hot glue on the plastic tab holding the circuit board to prevent any movement.
– to close the alarm back, I also used the hot glue gun, and added some silicone sealant, just to make sure I had a perfect seal.
– to reinstall the bracket of the alarm, I use a new breakable bolt, the same that was used originally. I guess the flat bolt is an added security to make removing the alarm more difficult for a thief.
– I had also ordered some new blind rivets from volvo. The new ones are plastic instead of aluminum for the original ones.
– after reconnecting the car battery, I tested the alarm and everything is working fine.
I have an extra circuitboard I got from a junkyard before I attempted to fix mine as I suspected the the circuitboard was fried. That was not the case. It seems just the dead battery is enough to cause the alarm problem.