Is There A Chance Of A Battery Fire?
[AT] A body shop that I’ve use and also have good ties with the owners has just told me about three NSX’s that had come in with major front end fires. It seems that the battery holder shorted against the +(positive) terminal and this immediately found a ground path to the holder tie rods. From this point the negative cable overheats and then starts an electrical fire under the fan motor. One of the car’s was totaled and the other had major damage. It seems that the battery can shift if the holder isn’t tightened sufficiently during hard cornering. Eventually the positive terminal will come into contact with this plastic coated metal hold down and if it has a small cut or chaffe to bare metal, then it can short to ground. Everyone please check your battery hold down and make sure it’s sufficiently tight to keep the battery from shifting. Looking at the design doesn’t inspire much confidence so I plan on making some changes. My body shop has seen three cars and has heard of others. Let’s hope we don’t hear of any more.
Why Does The Battery Drain So Quickly?
[AW] With the car off, the whole system draws 48 mA. Ouch. This is enough to discharge a 60 A-hr battery in 9 weeks. I’m shocked! Shocked! <g> (BTW, I forgot to look up the actual A-hr rating of the stock battery; I’m assuming for now it’s at least 60).
Then I started pulling fuses (one at a time). The only ones that made any real difference were the three "lower" ones in the front fuse box:
Clock: reduced drain to 36 mA
Interior Lights: reduced drain to 36 mA (disables factory phone, I think).
Door Lock: reduced drain to 36 mA (my car has the remote entry option)
All three pulled at once: reduced drain to 12 mA. This would drain our hypothetical 60 A-hr battery in about 30 weeks. (That’s more like
it!). That's close enough to the self-discharge rate of an automotive lead-acid battery that you need to put on a charger or something to keep it alive anyway.
I also pulled all the interior-panel fuses and none had any particular effect. Then, unfortunately, I started on the engine bay fuses (most of the smaller ones are for the seats). I pulled a fuse ("AGC"? I need to look that one up) which triggered the door locks or something, and that blew the fuse in my meter, so the experiment was over for the day. But, having gotten us down to 12 mA I’m not sure I care where
the rest of the current is going.
So what I conclude from this is:
- A "normal" (assuming mine is, of course) NSX will drain it's battery in a few (6-12) weeks of sitting.
- You can "fix" this by pulling three fuses if you know you're going to let it sit. It just takes a minute and it disables circuits you don't absolutely "need" in order to use the car. Or, you can put a "long-term" charger on it. See FAQ Section 11 - Storage and Transportation for more information on battery chargers.
- I finally found something "wrong" with my NSX. <g>
Finally, there may not in fact be anything "wrong" with an NSX that drains the battery after sitting idle for a few months. In particular, if the battery were a little on the weak side, the "normal" 48 mA drain could have taken out the battery in 6 weeks. Or, if there is an alarm or something that draws 10-20 more mA installed, that would be enough to do it.
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