9v Battery saver


Old 08-09-10, 06:44 AM
daswede's Avatar
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Location: massachusetts
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9v Battery saver

I read where if you don't use one of these when changing out a battery on late model cars, you can have many problems with the computer memory having lost its power source(battery).
Any opinions here?

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Old 08-09-10, 06:58 AM
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Sounds like good advertising. I have changed MANY and the greatest aggrivation is that on some vehicles, the radio memory will be lost.
On some vehicles, there will be a slight reprogramming issue that will cause the engine to act a little "weard", but this is short lived.
If you want to be sure, you can connect a trickle charger to the CABLES of the vehicle while changing the battery.
Old 08-09-10, 08:24 AM
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Location: North Central Indiana
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batt saver

Not up on the new stuff but heard a friend tell of having a batt changed and they plugged in a power supply at the cigg lighter while removing the batt.
Old 08-09-10, 10:15 AM
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You *should* be able to change a battery on any vehicle and not have any problems like not being able to start the vehicle. That would be a terrible design if the vehicle no longer worked!

BUT... Vehicle computers do have memory and self testing/adjusting memory. And if you remove the battery connections, this memory is lost* (as well as other things like radio as said above).

*It is possible to design computers with memory which is not lost when power is removed. I don't know if some vehicles are this way or not?

So far as the self testing portion of memory, part of this is for emissions testing. And some vehicle self tests only occur under certain temperatures, altitude, or driving conditions. Or the vehicle needs to start/cool down, then start again and maybe do this 3 times, then the vehicle test is "complete" and will be marked as a "completed test" in the vehicle computer.

And if you take your vehicle to be emission tested, and all those self tests have not completed, then they may not pass your vehicle. (They will connect a cable to your vehicle computer to see that the emissions self tests have run and passed.)

So if you are about to get your vehicle emission tested, not a good idea to change the battery! (Or keep a constant 12 volts on the vehicle as mentioned above, then the memory will not be lost.)

If you do lose your memory and fail an emissions test because all the self tests have not run, then here is a Ford example of how to drive your vehicle to get all the emissions self tests to run...
Ford Motor Company Driving Cycle

For some vehicle maintenance problems, you need to "reboot" the vehicle computers. This is done by removing the battery for 10 minutes, then reconnecting.

And when changing something like an oxygen sensor, it is recommended that you disconnect the battery so the engine computer will quickly adapt to the new sensor.

So if you have emissions testing and also a vehicle problem... Darned if you do, darned if you don't!
Old 08-09-10, 11:13 AM
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Theres no reason to buy some fancy thing from the autoparts store. You can make one from some wire and alligator clips and a 9v battery. Or dig in your spare plugs and cables and get a cig lighter plug, measure the polarity on the wires and use that and a 9V cell.

It can save hassle and frustration. My car has 20 programmed in stations and the preferred EQ settings...so it would take quite a while to get those back. Some of them are for other cities, so I would need to wait til I go there to finish up.
Old 08-09-10, 12:47 PM
Join Date: Oct 2008
Posts: 1,312
I type up a reminder list for my car and truck, then print it out and stick it in the glove compartment.

One of the things on the list is all the radio station settings, then I can easily reset them.

And how to change the clock. I can never remember this when daylight savings change comes around!

Other things on list...
I put the year, make, model, VIN, transmission, engine size, etc. Then when I go to the parts counter and they ask 3 zillion questions, I have all the info there on my list.

Wiper blade replacement sizes.

Then part numbers for each auto parts store. Like...
Air filter xxx
Oil filter xxx
Spark plug xxx

Air filter xxx
Oil filter xxx
Spark plug xxx

Makes life a LOT easier!
Old 08-09-10, 03:11 PM
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Wrench, it will work from the lighter, but the ignition must be on in order for the circuit to be complete to the accessories.
Old 08-09-10, 04:59 PM
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Originally Posted by chandler View Post
Wrench, it will work from the lighter, but the ignition must be on in order for the circuit to be complete to the accessories.
That's the reason I suggested to use the connection to battery cables
Old 08-10-10, 05:38 AM
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Nobody mentioned the security code for the radio if it has one. Make sure you know it/have it before you disconnect without "saver" power.
Old 08-10-10, 09:54 AM
Join Date: Jul 2006
Location: Virginia Beach
Posts: 221
My inlaw just went thru this with his Jetta after his battery went dead. Advanvce Auto said they wouldn't change it due to the computer etc. He ended up taking it to the VW dealership to change out. Never heard of anything like this before. And now just today I read this post. Interesting.

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