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Positive battery terminal ridiculously close to steel hold-down?

Hmmm. The only service manual I have so far (1991, page 23-67) shows the bracket mounted with the bigger side on top, positioning it closer to the battery terminals.

However, if it was mounted the other way as you suggest (technically incorrect according to the manual), there might be a little more clearance. I'll try that, thanks.
The illustration in the 1991 service manual is wrong!

Found this thread, and the parts diagram in it shows the battery clamp positioned as you suggest, providing more room around the battery terminal.
This illustration (from the parts diagram) shows the CORRECT orientation for the top hold down bracket.

battery hold down.jpg
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Good catch.

The service manual (at least right up to the 1997 service manual) shows the hold down inverted relative to the depiction in the parts manual. Pretty sure mine is is installed as per the parts manual.

Also, since you are presumably new to ownership, check your battery size. I expect that a lot of NSXs have drifted from the OEM size which can complicate the correct positioning of the hold down.
Part #2 in the diagram above shows that the longer cut-out is what sits atop the battery, so the metal is further away from the terminals of a correctly-sized battery.. The stability from the tie-rods comes from the three intersecting (near) right-angles of metal at the corners. As the battery is taller than it is wide there is more metal on the vertical face of the bracket than the horizontal face.
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Another thing to watch out for on the NSX is that people (usually service techs) overtighten the terminal clamps, which stretches/warps the soft metal and ensures your terminals will never clamp tight again. Kaz has a helpful tip on how to gauge the tightness here:

Also, if your clamps don't fit tight on the battery, I discovered these shims made to fix that. Ordered them today.

If your OEM battery clamps no longer fit tightly on the battery posts it is because a previous owner or service tech was over enthusiastic in tightening down the clamps (more is better - right?). If you get down for a close up examination (always fun with the NSX battery location) you will find that the clamps have likely been stretched and the metal is starting to tear / crack around the holes for the clamp bolt. Been there, done that, got the Tee shirt. Those lead shims will provide a fix which may last; but only if you are super careful in tightening the clamps in the future.

The better plan is to plan for re termination of the battery cables with some more durable battery clamps which is another fun NSX activity considering the accessibility of the battery cables. Having done this from the top, if you have access to a hoist it is probably easier to detach the cables and then access the ends for re termination from below the car. Fix the + cable before it gets damaged because a replacement is quite expensive.
I think mine had been wrapped with electrical tape from the previous owner. Just to be extra careful there is no contact. I'm sure you could spray it with some rubberized insulator or plasti-dip (not the spray) as well.
For all owners with the OEM battery: just make sure to clean the area around the positiv terminal otherwise leakage current is possible.
Depending on the battery you install, maybe flexing some material off might help.
The stuff I used was a dry plastic powder. You clean the metal, heat it up over a flame or the like, sprinkle or dip the metal into the powder, then heat again to smooth the finish. Additional coats can be applied to build up the thickness. Mine has been OK for about 10 years.
If you've gone to a Zanardi battery (51R) to save 10 lbs, you can 3D print a non-conductive battery holder that completely avoids the shorting problem, and also saves a pound over the OEM bar.

I did this 3 years ago and it's been great.
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