faifai83

I've replaced the battery twice on my 4GS and had no issues.

Have you tried detaching and reattaching the battery?

gadgetman1

Is it possible that the battery change triggered an anti-theft protection system within the infotainment system? I had that happen with a Honda Accord when the battery died. The radio was completely dead. Unfortunately, I didn’t have the activation code as it was packed in military storage, as I had just moved. I had to take it to the dealer & was fortunate that they believed me since I was in uniform.

leowaner

Agree with above comment......

Notwithstanding "holding voltage while changing a battery" is certainly a sound approach.... the comment above... e.g. letting the system "reboot" after the new battery is connected is CRITICAL, before restarting the engine. This is true on a push button start Lexus vehicle.... push the START button without the brake depressed and let the electronics in the car "reboot".... generally the Lexus banner will come up .... and other screens... that I can't recall right now. When changing batteries, they recommend letting the car sit after turned off for 2-5 minutes to let the operating data be written to both the internal disk drive and/or the system RAM.... BEFORE the "bad battery" is disconnected. That is why the "holding voltage" approach will allow you to keep all of your maps' prior map locations, radio stations, and other volatile data..... which will be lost if battery's power is disconnected, without a temp charge applied.

imjohnphan

I wouldn't recommend using a battery charger to maintain the voltage in a system without the battery connected. The battery in a way acts as a buffer and some chargers put out way higher voltage with no battery. My Schumacher 12V car battery charger will output around 17V not connected to the battery at all. Maintaining the voltage from something else more stable like another car or something else that puts out 12-14V should be fine but a car battery charger from the 2 I have tried puts out a high voltage with no battery connected.

With that in mind I changed out my 4th gen GS battery with navigation just fine the normal way without maintaining power. Just swap batteries with car powered off.

To the OP, maybe try unhooking the battery and completely discharging your car by touching the car (+) cable to the chassis (ground) for like 10 seconds. DO NOT DO THIS WITH THE BATTERY. And then go into the car hold the start button for a little while and then try to hold the power button of the radio for a little while. Then hooking back the cables to the battery and seeing if there is any difference. The hard drive may be corrupted or failed which would be unfortunate.

jonathancl

I don't think that applies to our radios: I replaced mine with one bought on eBay, and there was no special code to enter or anything.

arosnes

Connecting a power pack or an extra battery can cause sparks. Sparks is the same as high current, and high current can lead to voltage spikes.
Sounds like fried electronics...

currancchs

Not sure that I completely agree here. While maintaining power to the battery terminal connectors will certainly avoid the need to reprogram automatic windows, input radio codes, etc. and will also result in the ECU retaining learned parameters (this should result in the car running better, relative to battery disconnection, immediately after the swap, but these parameters will be re-learned in short order in any case), I do not believe that this makes it less likely that you'll have something fail during a battery swap. I say this because dealing with live jumper or charging cables while trying to remove a heavy battery from a relatively cramped location makes it substantially more likely, in my opinion, that you will accidentally short something out. If you do short something doing this, that has a far higher chance of damaging electronics than just removing the cables completely. Mechanics sometimes keep power to the terminals because customers often lose radio and other codes and wind up getting annoyed at the mechanic for "screwing up" their car.

Also, your technique will not work with all battery chargers, only the old ones that supply power without first checking for a minimum voltage and the new ones that have a "supply mode" option (i.e. a "smart charger" without a "supply mode" option couldn't be used). All of the options that do work will not prevent you from accidentally reversing the connections and shorting something.

Lastly, there is simply no way that disconnecting a battery will cause the "engine [to] perform... very poorly because MAF needs cleaning". If the engine does in fact run poorly after you disconnect the battery and runs better following cleaning of the MAF sensor, you had a dirty MAF all along that the ECU adjusted fueling to compensate for. When you removed the battery, the compensation was lost, resulting in poor running until the ECU again learns to adjust to the dirty sensor. Since this is something that should be taken care of, instead of relying on learned corrections to compensate for, this isn't really a downside to disconnecting the battery, you've actually gained valuable information by doing so (looking at fuel trims would be the usual way to begin diagnosing such issues, among others)! Furthermore, this condition should self-correct in short order.

drgrant

Just be aware after you do it (as peasodos describes) that the first time you start the car up it will probably stumble and stall once. This is normal. Wait a few seconds and restart it again, and it will probably be fine, let the motor run a few minutes and the ECU will finish relearning things enough to run mostly right, and that's the end of that.

-Mike

nallis

Just changed my battery and was wondering if I needed to keep voltage. Could not find an answer online. So I called a friend at the Lexus dealership and he said go ahead. It's not needed and they don't do it at the shop. I went ahead and no problems. Car only hesitant to start on first attempt but second attempt all is well.

However, I have come to my car already and started and got a dead Navi screen for a few minutes. Turned it off in traffic and it came back. It has done that two or three times in the last year.

HewittTech

You either zapped it with your cheap little boost pack or the battery leads were accidentally reversed even if all they did was touch for a moment. I have seen those cheap boost packs put out anywhere from 24-48V and damage things just like hooking a battery up in reverse.
I have seen both things damage sensors, radios and brick ECMs. Some vehicles can even be damaged by normal jump starting if you don't follow the correct procedure.
Be glad it was just the radio and replace it. You will not get anywhere trying to blame it on pepboys.

bclexus

Some battery chargers are not properly voltage-limited on the high side - meaning that when the charger is connected to a load (i.e. drained battery) the charger can deliver significantly higher voltage (either momentarily or for a period of time) above what may be considered safe for a battery and also for a vehicles' electrical system. This higher voltage could possibly cause damage to one or more of the vehicle's many electrical/electronic system components. (Battery minders, tenders, jump-starters and boosters are probably not the best choice to use to maintain voltage on a vehicle's electrical system when replacing the battery.)

As a couple of people have mentioned, by design not all battery chargers will supply a voltage when there is not enough of a load (e.g. drained battery) connected to the charger. If the vehicle's electrical system's current draw is below the minimum threshold of the battery charger's design circuitry, the battery charger may essentially go to a standby mode where it does not supply any measurable voltage/charging. Therefore, if the load of the vehicle's electrical system alone (with the vehicle's battery disconnected due to it being replaced) falls below the minimum load in which the charger will supply charging, attempting to use such a battery charger to supply and maintain voltage on the vehicle's electrical system while replacing the battery would not work.

Lastly, it should be no surprise that replacing a vehicle's battery without maintaining voltage on the vehicle's electrical systems is usually accomplished without any problems. However, there are enough times that people do experience problems after replacing their battery without maintaining voltage on the vehicle's electrical system. Many of these problems can be expensive and time consuming that necessitate visiting the dealer's service department, either by driving the vehicle there or by needing it to be towed there because [for example] the automatic emergency brake fails to release or an already dirty Mass Air Flow (MAF) sensor prevents the engine from starting because the engine's ECU resets and requires the dirty MAF sensor to be cleaned.

Here is a brief article about How To Keep Car Memory When Changing Battery.

Here is the Memory Saver (sold by Pep Boys) that Pep Boys should have used when replacing the OP's battery.

Self contained 12V OBDII Memory saver device
preserves codes, settings and memory in on-board
devices during battery disconnect.

sheez1

Pepboys would not touch my Lexus

charley95

When swapping a battery, would a Battery Tender work to maintain the memory BC?

bclexus

It depends on whether the battery tender specifically states it can be used to preserve codes/settings and memory in on-board devices (might be stated differently, but means the same thing). It's important to understand that you need a power source when your vehicle's battery is disconnected (as you are replacing the battery), so whatever device you use to maintain the vehicle's voltage must be able to supply power when your vehicle is WITHOUT its battery.

A battery tender has circuitry that detects how much of a charge the battery needs. It's purpose is to slowly trickle-charge the battery over a period of several hours. It has circuitry that stops trickle-charging once the battery is fully charged. The result is that a battery tender won’t overcharge the battery like a regular battery charger might (depending on the charger's circuitry). Some of the more expensive battery chargers have excellent circuitry design to prevent over-charging and the like, where others don't and can actually damage a battery if left to charge too long.

If your battery tender does not specifically state that it can be used to maintain (preserve) a vehicle's codes/memories/electronic presets/settings I would not use it in an attempt to accomplish that task. If you want to make sure to maintain power on the car's electrical system I would recommend buying an inexpensive ($11.00 from Amazon.com) OBD cable with battery clamps - plug it into the OBD port on your car and clamp the cable clamps to another vehicle's battery temporarily while you remove and replace your car's battery. Slick and easy, and no chance of anything going wrong.

charley95

That's good to know. Thanks BC!