Battery drain when storing your car.

[jaffaz32]

Not everyone has access to a battery tender due to electric hook up etc.

Just a idea, but these may be worth a try?

http://www.ebay.co.uk/itm/2-Auto-Ba...r_Truck_Parts_Accessories&hash=item5652bd573d

park your car up, twist and no drain.

This is my disclaimer if anyone thinks this is a good idea, the electrics having no power feed may be a bad idea, someone please correct me if this is the case. No power may reset settings, electronics, control boxes, ecu etc. It may not, i don't really know, was just a idea. Stumbled across them looking for something else.

 

[synergy004]

I use a battery disconnect switch/isolator switch from moroso. Same concept as the one you linked.

 

[Old Guy]

Disconnecting the battery will result in the loss of the radio presets for tuning and the clock setting. If the ECU had trapped any error codes, you will also lose the record of those error codes. I believe the error code has to come up three times before the MIL indicator will light up so you might have error codes that you were unaware of - should not be a problem if the error is not repeating. All of this is a minor inconvenience compared to a dead battery.

Some people have suggested that when the factory ECU goes into closed loop operation and starts adjusting the injector timing to bring the A/F within target (if it is outside of the target A/F ratio), it stores those revised settings in memory for future use. This real time correction of the A/F ratio is referred to as trim. Most, (all?) contemporary fuel injection systems that I am aware of do closed loop trim. However, I have not seen anything in the NSX service manual (or any documentation elsewhere) that suggests that these trim settings are saved in memory for future use. In the systems that I have seen that have open software (there is deffinitely nothing open source about the NSX ECU!), the trim is a real time feedback system used to correct the A/F ratio and the trim values are not saved.

Note that there are (or were) some aftermarket ECUs that claimed to 'learn' the vehicle (populate the base fuel map using the O2 feedback signal in a learning mode). This is something totally different than the trim in closed loop operation.

Short answer - you can disconnect your battery with impunity.

 

[nsxtasy]

Battery disconnects have been discussed here extensively. There are a couple of problems, though, in addition to those already mentioned. The battery is inconveniently located in the NSX, especially for those who use the spare tire, so reaching down to it is not necessarily just a 20-second operation the way it is in many other cars. Also, if you disconnect the battery, your security system is disconnected. Maybe you aren't worried about theft (either of the car or its equipment or contents), but many owners are. Furthermore, this is typically a much greater concern for those who don't have a private garage at home (such as those parking in high-rise condos/apartments), the very same owners that typically don't have a nearby source of power for a charger. If your car isn't there when you return to it, that's not exactly "impunity" from harm!

 

[warrenw]

I disconnect the battery on my S2000 for 6 months every year. There isn't any power available at the parking site.
Everything is lost like:
radio presets (I record them every time)
ECU info ( it takes one tank of fuel for the system to re learn )
radio security code (NSX does not have this)
Alarm system is disabled ( the car is in a secure condo parade )

the car starts right up every spring.

 

[Grimeas]

You would only need one of these. They were on my car when i bought it and became an extra source of crappy/dirty/loose connection that made my car not start. I take the extra 5 mins and grab a 10mm and just disconnect the battery without the quick D/C when my car will be sitting more then a few weeks.

 

[BATMANs]

I tried that and the way it's designed didn't give the most connectivity and sometimes it would unscrew loose for some reason.

The metal is soft and I was none the less dissappointed.

It was with the RX7 years ago.

 

[gene '96 #178]

Not sure of this but thinking from my memory....
Isn't there a plug that you can put into your cigarette lighter receptacle (that takes a 9 volt battery) which will keep you from loosing the info posted?
Not sure, just saying what I've seen in catalogs........

 

[Old Guy]

Disconnecting the battery will result in the loss of the radio presets for tuning and the clock setting. If the ECU had trapped any error codes, you will also lose the record of those error codes. I believe the error code has to come up three times before the MIL indicator will light up so you might have error codes that you were unaware of - should not be a problem if the error is not repeating. All of this is a minor inconvenience compared to a dead battery.

Some people have suggested that when the factory ECU goes into closed loop operation and starts adjusting the injector timing to bring the A/F within target (if it is outside of the target A/F ratio), it stores those revised settings in memory for future use. This real time correction of the A/F ratio is referred to as trim. Most, (all?) contemporary fuel injection systems that I am aware of do closed loop trim. However, I have not seen anything in the NSX service manual (or any documentation elsewhere) that suggests that these trim settings are saved in memory for future use. In the systems that I have seen that have open software (there is deffinitely nothing open source about the NSX ECU!), the trim is a real time feedback system used to correct the A/F ratio and the trim values are not saved.

Note that there are (or were) some aftermarket ECUs that claimed to 'learn' the vehicle (populate the base fuel map using the O2 feedback signal in a learning mode). This is something totally different than the trim in closed loop operation.

Short answer - you can disconnect your battery with impunity.

Before I get flamed!

I need to make some corrections to my comments on loss of data in the ECU when you disconnect the battery. Following my post, I was having a discussion with a friend about ECU operation and fuel trim. He noted that some (maybe all) Fords and GMs retain long term fuel trim (but not short term trim) in memory and use it to modify the base fuel map to correct for long term aging or other factors which may alter the air/fuel ratio. He thinks that the Fords had a long term fuel trim map that had a long term fuel trim value that corresponded to every value in the base fuel map (be interesting to know how long it would take for the ECU to populate a complete table like that!). He believes that the long term fuel trim is used to alter the injector duration pulses even when the ECU is not operating in closed loop mode (during start up, wide open throttle and power enrichment). When the ECU goes into closed loop operation, the injector pulse width is determined by the combination of the base map value added to the stored long term fuel trim value and the current calculated short term fuel trim value.

I still can find no reference in the NSX service manual to the ECU storing and using long term fuel trim values to modify the base fuel map. The only reference I can find in the service manual is:
Long term fuel trim in computed from short term fuel
trim and indicates changes occuring in the fuel supply
system over a long period.
If long term fuel trim is higher than 1.00, the amount of
injected fuel must be increased. If it is lower than 1.00,
the amount of injected fuel must be reduced.

However, after a little searching, I came across what appears to be some Totyota training material that definitely references using a stored value of long term fuel trim to modify the basic injector duration calculations in both closed and open loop operation. The Toyota material is non specific but seems to imply that only a single value of long term trim is retained in the ECU. So, if Toyota is doing it, its probably a safe bet that Honda also does it.

So, this is probably no big deal, unless you have made some material modifications to your engine which affect its volumetric efficiency and are still running the stock ECU. The NSX service manual states that the long term fuel trim can be between -19% (shorter pulse width) and +25% (longer pulse width) before throwing a code. If you have made some modifications which are causing the ECU to run with a long term fuel trim close to 25% and you erase that value by disconnecting the battery, it is possible that you may encounter some initial drivability issues on reconnection of the battery until the car goes into closed loop operation and has been in operation long enough to repopulate the memory with a long term fuel trim value. I have never experienced this; however, my car is box stock and I expect that the long term trim value is probably close to 1.00.

 

[greenberet]

To the OP: the battery quick disconnect you linked to in post #1 looks like the one I installed in my NSX a few years ago. I’ve been so happy with it that I installed it in my other cars as well.

The NSX service manual states that the long term fuel trim can be between -19% (shorter pulse width) and +25% (longer pulse width) before throwing a code.

Great find! What page is that on?

 

[Russ]

The NSX shop manual starts off many procedures with "Disconnect battery." No big deal.

Maybe a solar panel that plugs into the cig lighter? Might not work too well in a garage though.