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Battery Dead Overtime or Main Relay is Broken?

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All,

I have a 97 that I usually drive every two weeks or so. When it's more than two weeks, the car usually wouldn't start, and I think it's because the battery is dead. Not sure if it's a dead battery or the main relay switch. The status light indicator turns on when I switch the key to ON position. Once I twist the key to start, it cranks but becomes the noise becomes weaker and the status lights turns off. I think it's the battery.

If it's the battery, does anyone have this problem? After two weeks or so, the battery just dies. I'm wondering if there's something ya'll might know that could be draining the battery while off. My '00 ITR doesn't have this problem.
 
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On a non Zanardi version, the original sized battery should allow the car to sit for two weeks and restart successfully. That assumes that the car is stock - no after market security system or stereo system. If the car has been fitted with a light weight battery it will likely not make it two weeks. How many times have you allowed the battery to discharge to the point that it will not start? Each time you deep cycle a battery you shorten its life. If you have deep cycled the battery four or five times the battery may be at the end of its useful life, particularly if the battery is already 4 - 5 years old.

If you can jump start the car with an external battery / booster pack, then the main relay is just fine.

The dash cluster has a voltmeter on it. Watch the voltmeter as you engage the starter motor to crank the engine. If it is dropping below 10 volts you have a battery that has exceeded its best before date or your battery post clamps have failed (or both). Loose battery post clamps are a not uncommon problem on the NSX caused by people overtightening the clamps and stretching them to the point that they no longer tightly grab the battery post.

Have your battery load tested. If it fails the load test, install a new full sized battery and check the condition of your battery post clamps. If the car will not restart after two weeks and you do not have any aftermarket stuff on the car, then you may have a high parasitic load due to an electrical problem in the car. However, that would be super rare.

My stock 2000 NSX with the original sized battery will restart just fine after sitting for two weeks
 
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Thanks. My car is bone stock.

I can jump start the car with an external battery / booster pack, so the main relay is just fine.

I think with two weeks, the car usually can start, but if it's after two weeks then it tends to die. It's not all dead, but mostly dead (i.e. the clock is still good and engine lights are on, but not enough power to to turn the engine on). What's annoying is that when this happens, the O2S, CAT, and EVA data are reset, so it's a pain to get them back for the smog check.

Is more than two weeks expected? Does anyone use a trickle charger? Any recommendation for the brand.

My experience with trickle charger in the past is that it didn't work with my ITR.
 
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A bone stock NSX has about a -0.5A drain when it is shut off and locked. This is mostly due to the security system, but there are also other modules like the ECU and radio that use battery power to keep their internal memory active. Two weeks on a healthy battery is usually not enough to drain it. That said, most NSX owners use a battery maintainer when they put their cars away for an extended period. It sounds like your battery is dead. I'd get a new one and keep it on a maintainer when it is going to sit for more than a couple weeks.
 
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A bone stock NSX has about a -0.5A drain when it is shut off and locked. This is mostly due to the security system, but there are also other modules like the ECU and radio that use battery power to keep their internal memory active. Two weeks on a healthy battery is usually not enough to drain it. That said, most NSX owners use a battery maintainer when they put their cars away for an extended period. It sounds like your battery is dead. I'd get a new one and keep it on a maintainer when it is going to sit for more than a couple weeks.
Thanks. Any recommendation for the battery maintainer?
 
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A bone stock NSX has about a -0.5A drain when it is shut off and locked. This is mostly due to the security system, but there are also other modules like the ECU and radio that use battery power to keep their internal memory active..

I think Honcho might have slipped a decimal point. About 4 -5 years ago the issue of dead batteries and parasitic current load came up on the forum. Out of curiosity, I went out and hooked my Fluke digital multimeter in series with the ground cable on the battery. On my 2000 with keyless entry the quiescent unlocked current was a around 0.05 amps . The surprise was that when I locked the car with the security system armed the quiescent current remained at 0.05 amps. Unlike building security systems that continuously circulate current through the perimeter contacts, the NSX system must rely on voltage supervision which has a lower load. So, storing the car armed or disarmed would not appear to materially alter battery drain.

When you first connect the battery there is a high parasitic current of about 0.150 - 0.200 A. This tapers to about the 0.05 A range in less than 1 minute. That is what I measured with my multimeter on my car.

Short answer, with a good battery on a stock car you should easily be able to go 2 weeks between restarts without a battery tender.

I think my Audi A4 is probably an all time winner for parasitic load currents. On initial shut down the parasitic load current can be around 8 amps because of things like the turbo after run coolant pump. It does taper off after a few minutes; but, still remains fairly high because of crap like the 4G module and other stuff. CTEK chargers are sold by and highly recommended Audi if you don't use your car extremely regularly.
 
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I had it plugged its battery connected to the trickle charger, and the battery still went dead. Could be the brand of the trickle charger (or the battery).
If you have deep cycled the battery on more than a few occasions sulfation occurs and the battery may no longer accept charge. Some battery chargers and maintainers have an anti sulfating function (my CTEK for my Audi A4 claims to have an anti sulphating cycle). I don't really now how well these work.

Short answer, if the battery has been deep cycled and has developed sulfation at the plates it may be a goner and no amount of time on a trickle charger may fix that problem. AGM batteries are said to be more tolerant of being deep cycled and more resistant to sulfation than conventional flooded cell batteries - that is internet wisdom so treat appropriately.
 
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