Replace dead battery on lexus ls460
 

Can i start the car and leave running and then replace the dead battery to prevent losing all my electronic phone contacts and Nav points?

NO: The battery must be IN the circuit while the engine is running, even if it's dead. Remove it while the engine is running and you will have more problems than just a dead battery. :look: NB

BTW: I strongly suspect that your GPS/NAV system has backup capability to allow changing battery's just like my 10 year old handheld Magellan GPS. There is a time limit on my Magellan..say an hour or so, that maintains the memory while you change battery's.

Check your car owners manual. :) NB

I'd for sure order beef, and probably with a red wine but possibly with a woody white. Not at all sure about the battery part, I might skip that altogether.

At my side business if we need to disconnect the battery I have made up a small box that holds a nine volt battery. Connected to the box is a cigarette lighter accessory cord. We plug the box via the accessory cord into the cigarette lighter and the nine volts holds the vehicle computer, radio and accessory device needs until we replace or reconnect the battery.

I built mine but I have seen the same device available in many auto parts stores for about ten bucks.

Handy little tool to have!

Do they take reservations?

Found this and it seems to work
http://www.tayna.co.uk/tutorials/cha...radio-code.php

YES: This would work. HOWEVER..there is a very good risk you will strike "Ground" with the HOT wire while you are doing this. Your original question indicates you are a Novice. I would not recommend a Novice DO this procedure. No disrespect intended.

SKIPS procedure is much safer...because there is no risk of striking and ARC. However: I would use a 12 volt battery.

I would like to hear Skip explain how mating a 9 volt dry cell with a 12 volt wet cell would work. I am thinking the 12 volt wet cell..the car battery..no matter how low in voltage, would likely try to Charge the 9 volt dry cell. Dry cell battery's don't like to be Re-Charged. I think they explode. Just wondering..:look: NB

PS: When you mate two battery's together which have different voltages.. the battery's TRY to equalize. That means the battery with the greater voltage trys to bring the battery with the lesser voltage into.."Equalibrium".

The 9 volt device I built is diode protected so the 12 volt battery cannot damage it. Someone with basic electronics skill can easily build one, but I would still recommend a layman pick up a manufactured version of this device at a local auto parts store for the reasons you pointed out.

Thanks....

Skip, even the diode won't protect you. In fact, with our automotive parts we design many of them with undervoltage lock-out (and other protection schemes) to prevent users from damaging parts doing exactly what you are doing.

My advise is never power up an automotive system under 12V. You can create walking wounded devices as well.

On my current project, I'd say 30% of the design is the protection scheme (undervolt, short circuit, etc). You're welcome;)

Hey, I know someone who totaled their Audi TT big-bucks sports car, and blames it on the talking navigation system. He drove it down a Rt 95 highway exit in Burlington, Mass, got a little confused which way to turn, was listening and thinking on the talking directions, and drove onto the grass at the exit and struck a large flat boulder that ripped into the underneath of the Audi....... and it got insurance 'totalled.'

Best to just stop at the local Irving or Mobil and purchase a map, and forget about these talking nav systems! If Christopher Columbus had a talking nav system, he would have stopped in Cuba, and never made it to the United States!

Wow
 

I thanked SKIP for his last post but I guess I got carried away. :D :D NB

"The Following 4,294,967,295 Users
Say Thank You to Skip
For This Useful Post:"

Did you ask the Lexus dealership service department?

The correct answer was given in the first response by NoBozo......

I'd fully suspect that the OP would pop one or several fuses if he did what he asked if he could do.

BTW: NOBODY that owns a Lexus LS460 replaces their own battery. Just not happening. They Have People for that. :D NB

We have a LS460 and the dealer disconnected the battery. The GPS system kept our settings but the Radio settings were erased. I was not aware how much we were programmed to our favorite stations. I would ask Lexus to do the work. The car can only be 5 years young.

I would expect the nav system to not loose its memory. The Radio on the other hand will go the way it goes... Some radios will save station presets some will not.... Mine I know for a fact does... so does the one in my boat....

As for any of the work arounds here, etc. that I keep reading... I recomend none of them... No offense guys... but the link for using a secondary battery in parallel??? that is asking for a problem, and with the electronics in the cars today you are asking for an even bigger problem.... As for the 9V solution... I would like to understand more about this? but quite frankly I think your fooling yourself thinking that a 9V battern is keep your memory alive....

I remember my first car's radio presets. I had to pull out one of the five buttons and push it in once I found one of my favourites. It was the only thing on that thing that worked properly (1969 MGB-GT). At least you could disconnect the batteries (2-6V) and still have your presets.

I am Saddened that the Webmaster has seen fit to deprive SKIP of the over 4
Billion members who Thanked him for his post. :D NB

The problem with this type of setup is you have numerous parts with regulation and blocking. 9V is several diode drops below 12V. In most cases we assume voltage dropping to maybe the 9.8V range.

The reason why people think it works is we overbuild our designs. Period. However all our devices have given current density limitations through subtrate contacts to ground. Current actually flows from - to + as some of you probably recall.

Take 3V across a low ohmic contact and guess what happens during that transient? Look at the simple equation for capacitor current and doing this is ugly. A parasitic BJT in a power MOSFET only needs 0.7V to turn on and destroy itselt.

If you over power the contacts you can get electromigration. If in a radio, this can cause issues that may not be destructive but could be subtle. Phase locked loops can get out of whack, reception range effected, you name it. You may not think you did damage but you did.

In design we see the field returns and get to understand failure modes. Nothing is fool-proof as hard as we try. We never do biased reliability testing at 9V for auto applications which should tell you something.

Many technicians will claim I am full of it because they "get away with it". However as a designer of high power applications with automotive and appliance products this is terrible practice. We have to put stuff in our designs just so that when people do bad things to parts we can demonstrate why the failure was user related and not our part. This is also why warranty claims get denied.

In todays systems we have a lot of detection systems to look for shorts and undervoltage protection because it's such an issue. Most of the issues are from the assembly process and when maintenance is done on the car.

Off too bed. zzzzzz

You can also simply take a 12 volt jump pack and plug into a power port change the battery no harm no foul. After over 30 years in the repair busines never had an issue with using a 9 volt into a power port to retain memory or driveability controls I wouldn't count it as lucky but proven works with no issues.

Could you imagine if radios or other car electronics were real easy to damage by putting 9 volts across them? Every winter there would be a rash of dead electronics. How many here have cranked that the starter on a cold winter morning and seen the lights dim, thats your voltage dropping. If you crank a little too long you can get to 9 volts, pretty easy, give it a try.

Now I don't know if a 9 volt battery has enough voltage to save the memory in every case, but I would guess so, semiconductor memory is very tolerant to voltage. But that little 9 volt battery is not going to damage anything, especially a parasitic junction in power MOSFET. You would have to try very hard to make a circuit that would work reliably on a nominal 12 car battery but be damaged by a 9 volt transitor battery.

jrc, mostly likely there's a clue to your question everytime you start your car.

Turn on ignition and radio but don't start car. Now start the car. Did radio stay on? Hmm, wonder why that would be;)

For the starting application the system voltage is uniform. For damage to occur on devices you need the relative voltages to be different.

Draw a fish diagram of a car battery system and everything hooked up to it. Now draw in a 9V "capacitor" to the system through a switch which is basically what the memory hold device is when you plug it in. Close the switch and tell me what the current and voltage transient would be.

Car techs can scoff but there is numerous reasons manufacturers state in the manual to disconnect the battery prior to working on the electrical system.

When we work on parts on the bench during development, it's very common for us to misconfigure the bench set-up such as turning power supply knob wrong way, forgetting to set current/voltage clamps, and other stupid things we do (we're human). It's not uncommon for a part your working on that was reading perfectly to "change" when you do make a set-up mistake. Part may still function but now it's out of datasheet spec or a host of other weird peformance issues. Bad design? Maybe, maybe not, but once you take a part and hit it with something it was not designed for all bets are off. Some of the changes are subtle.

Me, I would not touch my car with a 9V memory hold device. Best place to store it would be the garbage IMO. The reason you don't see widespread issues with people using the memory holds is largely due to the protection schemes inherent to the design.

If we really want to deep dive, "9V" batteries are 9V or all the way down into the 7V range versus a lead acid battery which is 12.5V+ with alternator not spinning. Thus, voltage differential in real world is higher than 3V....

The parasitic transistors on many parts in automotice system are referred to as the body diode. It's related to the dV/dt, not just steady state conditions (although they do apply). You decide if not having to reset your radio presets is worth the chance of doing something to your car.

Many manufacturers are now putting non-volatile memory on electronics. Way more details than I want to go into but you'll have to hash that out with the product and applications engineers if they should add it or not. Memory to hold ECM/PCM stuff is important. Radio presets, not so much. Cars get expensive $0.50 at a time so be careful about those seemingly trivial costs.

PS: No such animal as a transistor battery.

Lexus Battery
 

I thought if you owned a Lexus battery replacement would be done by your mechanic;)

PS transistor battery is is used just like kleenex, frigidar....People know what it means (or those of us old enough to have had pocket radio)

Transistor batteries are batteries originally designed to power transistor radios. Design in the 50's to fill the hole between flashlight batteries (AA, C, D) and 22 volt batteries for tube radios. There are no transistors in the battery. Just like there's no spaghetti in spaghetti sauce.

Fish diagrams, 9v capacitor? What are you talking about? Draw me a real circuit that can operate normally over the range of a 12 volt battery but will be damaged if a 9 volt transistor battery is applied. Never mind we are way off topic.

I know about transistor radios, never heard the term transistor battery.

Notice my "" around the 9V "capacitor". That's an important detail. Batteries actually pack some punch. A battery doesn't get it's energy from thin air. You have plates and a dielectric. In order to supply current, a battery must have charge (Q). The equation is Q = C * V and derive from there.

A fish diagram is what we use when taking chunks of a system drawing and represent what's hanging off the car electrical system. Look in a car electrical manual and you'll see why we have to do that since things can get crowded when viewing so we break things up, etc.

I've attached a simplistic drawing. Here's how the system is at risk using a 9V hold device. The battery is hooked hooked up and at 12.8V. 9V battery is attached with a diode to prevent the car battery from charging and destroying the 9V. The diode to the 9V battery is reveresed biased. All is well. Joe tech removes that car battery, does his thing. Radio presets are held. Battery is put back in car and hooked back up. When the battery is connected, the system is at the 9V (or there abouts) and the car battery is at 12.8V. That is a deltaV. So where does it go??? It's doesn't just magically disapper as you have Ic = C * dV/Dt to contend with (remember how a battery is a capacitor?). That is a surge and the current has to go somewhere until the diode can shut off (it's not instantaneous). In our designs we try and protect for both negative and positive spikes which is exactly what happens on the system. If a spike is too quick than you can cause damage to the input of devices connected to the 12V system.

Keep in mind semiconductor devices are subject to degradation with power cycling, temp cycling, changing moisture levels that the mold compound sees. Also, a lot of stuff is relayed on and off the electrical system for reason such as noise, loading, and transient protection reasons.

I am NOT saying 9V device = automatic damage. I am saying there is definite risk. Those transients can be quick. Faster than the proection devices can respond. How many people have damaged something when they jumped a car (correctly) or accidently shorted a screwdriver across the battery? Trust me when I tell you that you can damage parts of the car that can be latent issues causing parts to fail early or not as intended. Six months later when something goes because you whacked it with a surge you'll never even think is was from that time you jumped the car, etc. We have a non PC phrase we use when this condition occurs.

Lastly, I have attached Littlefuses (not the company I work for) arsenal of automotive electrical protection devices. You asked why there are not widespread issues with car electronics going bad, this is why. A car electrical system is quite nasty when you put an oscilloscope on it. The protection devices you see in that document are everywhere on you car because people plug in things like 9V memory hold devices;) Yes, the techs are being saved from themselves. In the end it's up to you folks to decide how to work on your car. I'm just trying to warn people that the potential to damage components in your car with a 9V battery gizmo (even the one's you buy or diode protect) exists.

I design power devices designed for automotice and appliance applications for a living and I would never use a 9V memory hold doo-dad.

Carry on. Last post on this topic.

Sorry, I know this has been off topic and not lake related, but I do drive my wife's Lexus to the lake once in awhile:):):)

One thing missing is that todays vehicle need more than 12 volts,if you check you altenator output i's more than 12 volts. I have used both in my years of experience a 9 volt and a 12 volt jump pack a per manufacturers instructions and guess what never an issue. With todays vehicles you can run into many issues when you remove all power from memory. Forget radio presets not really an issue,how about driveability relearns,readiness for inspection just to name a couple. IMHO,we're over complicating a simple task.

I replaced the battery in my wife's Tahoe and I didn't even lose a radio station. The key fob still works too. Surely the folks at Toyota thought of having to replace the battery sometime...