I am helping an older friend with her 2004 RX8. She's having parasitic drain so that her battery is going dead after 3-4 weeks. I pulled her battery and trickle charged it for over 20 hours and got it back up and now it's running again but I have a couple questions.

First, when I lifted the battery cover to remove the battery to charge it, I saw that whoever worked on it previously did not put back the battery hold down bracket. I see from mazda's parts diagram that it has a bracket that apparently hooks into the battery box on one side and then uses the typical hook bolt and nut to secure the other side. Mazda is proud of this part and wants about $50 for just the bracket. Does anyone know an aftermarket bracket that will work on this instead of paying $65 for the Mazda bracket and bolt?

Second, where should I start testing for this parasitic drain?

Thank you,
David in Arizona

 

I would hit the junkyard for fhe bracket. However 3-4 weeks of... not driving? That's pretty good. Expect about 2 weeks on a healthy 8.
I would go through the fuse box one by one and see where you find draw. Nominal healthy draw for the alarm and other sleeping systems is 10-20 milliamps.

 

She rarely takes the car out since it's not her daily driver. She had to be out of town for about 5 weeks recently, so it was dead again.
I'll check the fuse box.

However, I don't know what you mean by "That's pretty good" What's pretty good, it taking 3-4 weeks to for the battery be dead? And does "Expect about 2 weeks on a healthy 8" mean a healthy v-8 would drain it in 2 weeks?

 

A healthy RX-8 ("8") should be out of battery after sitting for 2-3 weeks. Most modern cars are like this, they have alarm systems and other always-on components. 5 weeks is really pushing it. Get her a trickle charger and/or a deep cycle battery.

If you want to check for phantom current, put an ammeter in series with the negative battery cable and give it a minute to stabilize. Make sure silly things like trunk light aren't on. If it stabilizes around 0.02 amp, this is normal. If it's higher, there is phantom drain somewhere and you can go fuse by fuse in the fusebox to isolate it.

 

Got it -- thanks for the clarification. I did install an automatic 2A trickle charger for her so hopefully the problem is solved.