I'm old school, back when I replaced the battery on my wife's '17, I did not use any sort of memory saver. Only thing I needed to do was reset the passenger side power window.

 

How did you reset powe window

 

Unfortunately our Fed Ex driver has the same mentality. if it's heavy or bulky, just toss it and leave.

There are a couple threads on memory savers...

(All Years) - Memory saver vs. battery charger vs. nothing?

Before doing a routine battery terminal cleaning job (my first for a Subaru), I searched the forum for advice on needing a "memory saver" anytime the battery was disconnected. I was aware that trivial things like radio presets and trip mileage would be lost, but non-trivial ECU's? I really...

www.subaruforester.org

('19+) - 2019 - Battery change and saved info?

I am about to change out the battery on my '19. Does anyone know if saved info (radio, seat position, sound selection, etc.) remains, or does it have to be reloaded after new battery install

www.subaruforester.org

Mods, feel free to delete this post if you merge...

 

The 12 volt ‘cigarette lighter' ports won’t work. They are controlled by battery powered relays. No battery, no connection between the port and the rest of the car.

If you don’t keep power up while the battery is disconnected, you could lose radio settings and window settings, and experience rough engine performance till it relearns. Nothing fatal, but an unnecessary hassle to have to deal with.

I use my jump start box to keep power on when changing the battery. Positive lead to the battery connector, ground lead to chassis. Be careful positive doesn’t accidentally short to ground during the procedure. Since everybody should already have a jump start box, no further investment is required.

 

Be careful positive doesn’t accidentally short to ground during the procedure.

^^ Worth repeating ^^

Here's what I use on my 2018:

Amazon.com: OBD ll Connector Vehicle Memory Saver Reliable and Easy 9 Volt Battery Powered : Automotive

Amazon.com: OBD ll Connector Vehicle Memory Saver Reliable and Easy 9 Volt Battery Powered : Automotive

www.amazon.com

 

Thanks for the insights. As far as the 12v memory keepers are concerned, I've read that you have to keep the key in ACC for them to work (and I've been told, "no you don't" -- arrghhh!). I don't have a jump start -- used to when I had unreliable cars, but haven't needed one for 20+ years. Maybe I'll get one anyway, if only to satisfy my gadget craving.

And thanks for those links, which led me to realize...the jury's still out. It's like on Amazon Q&As:
Q: Will this fit a 2018 Subaru Forester?
A: Yes.
A: No.

 

Thanks for the insights. As far as the 12v memory keepers are concerned, I've read that you have to keep the key in ACC for them to work (and I've been told, "no you don't" -- arrghhh!).

If you connect your alternate power supply to the battery terminals, to the car it just looks like a battery, so you don't have to do anything with the ignition. If you connect your alternate power supply to somewhere else on the wiring harness, you may need to have the ignition in the accessory position in order to connect where your power supply is connected, to the circuit you want to keep powered.

If you have kept all of the 12 V supplies from failed electronics that you haven't bothered fixing, just get one of those and connect it to the battery terminals, maybe through a diode, as you swap the battery. If you aren't comfortable or familiar with doing this sort of stuff, just swap the battery without the alternate power supply, and reset all your stuff later.

 

It's easy enough to do with a small 12v power supply. I built this thing dozens of years ago and been using it for battery changes since cars came with computers. Here it is in use in October on our 2018. As an electrical engineer I have a healthy respect for all that can go wrong when you mess with microprocessors. Rarely a week goes by without a new thread about someone who had a battery die or changed a battery and can't get something to reset properly.

Oh, and remember to follow the TSB with regards to how to safely remove the wires from the battery lugs to avoid having to replace broken sensors or fuse assemblies!

 

Can I just use a battery charger instead? I have a battery charger/tender. Where did you hook those up?

 

When I changed the battery on my '18, the only thing electrical that was lost was the synchronization of both front power windows.
Re-initializing them both took all of 10 seconds.
I wouldn't waste my time trying to keep the car's computers electrically energized while swapping batteries.
I can assure you that when the dealer is servicing the electrical system, they are not monkeying around with supplying continuous power.
They just disconnect the negative battery terminal, then re-connect it when done.
And from personal experience they have been known to forget to synchronize the front power windows before returning the car to the customer.

 

When I changed the battery on my '18, the only thing electrical that was lost was the synchronization of both front power windows.
Re-initializing them both took all of 10 seconds.
I wouldn't waste my time trying to keep the car's computers electrically energized while swapping batteries.

Hey, you do you. I'm good with that!

But like I said, not a week goes by in which a Subaru owner doesn't complain that something got messed up when power was interrupted.

Here's today's event: Unable to change TPMS from kPa to PSI

 

Be careful positive doesn’t accidentally short to ground during the procedure.
^^ Worth repeating ^^

Absolutely agree! That's why I built a 1 amp regulated power supply for this task and monitor it with a meter.

 

I'll reiterate that I had an '18 Forester, and had no issues other than power window synchronization after disconnecting the battery.
Just giving others a heads up that going to extremes to save electronic settings is not necessary.
The possibility of doing far more electrical damage to the vehicle by connecting up homebrew and eBay OBD power connectors is not worth it in my books.
But, "Hey, you do you. I'm good with that!" LOL

 

The possibility of doing far more electrical damage to the vehicle by connecting up homebrew and eBay OBD power connectors is not worth it in my books.

I glad that you had good luck and don't feel the need. From the postings others haven't been so lucky. We all cheat death until the day we don't....

I would NEVER recommend that you or anyone else do something outside of your comfort zone or field of expertise. If this scares you, walk away. Heck, drive to your nearest Autozone and have them do it for you.

I was comfortable enough to design and build my own fixed voltage current limited near ripple-free power supply that is perfect for keeping automotive electronics alive and happy in a standby state, and I know how to use it. But professionally I'm no stranger to automotive electronics design projects, so this is just second nature to me.

 

Heck, drive to your nearest Autozone and have them do it for you.

Around where I live, that’s a definition of living dangerously… Their toolkits generally consists of a screwdriver, pair of channel-lock pliers and a set of vice grips…

 

OK, bad example!

 

Watched a youtube video on changing the battery in my 2018 Forester, and for the first time heard about memory keepers. Say what? Seems it's to preserve the car's computer memory settings, of which I guess there are...lots.



So went about looking for one -- some people say you have to plug into the OBD 2 (say what?) and attach to an external power source, like another car battery or a jump starter.



Others say you just need one that plugs into the 12v port and attach a 9v battery to the memory keeper.



And others say you don't need to do any of that, just pull the old battery and pop in the new one, and you don't lose any of those settings. The Forester manual doesn't say anything about it that I could find.



So I found one at a local auto parts store -- the kind that plugs into the 12v port and uses a 9v battery for power (the battery will last about 2 hours, long enough...I hope).



This is all brand new to me -- haven't had to install a battery for decades (I'm of the generation who had VW Bugs with batteries under the rear seat that would start fires by connecting with the seat springs and/or fall through the rust holes in the floor onto the street.)



Somebody here must know about this stuff, and I'd appreciate some insights. If the car computer doesn't even need a memory keeper, that would be great, but if it does, will what I got do the job? Thanks. (I'll keep hoping that the 50-lb Odyssey battery that the FedEx driver dropped on the concrete floor with a resounding thud is OK -- no damage to the box, nothing visible on the outside of the battery, seems this battery is overbuilt for durability.)

The only thing I lost when I removed my battery on my 2014 Forester Limited was the radio station presets.

 

I have to disconnect the battery on my 2019 Forester when I tow it between FL and NY several times a year and the battery is disconnected for 2 days (the disconnect is needed to keep the steering wheel unlocked while on the tow dolly). I can confirm that the engine/transmission parameters need to be relearned after re-connection, but the vehicle does it pretty quickly. You also lose several settings, like the TPM system changes to KPa vice PSI. It's not a big issue.

 

OMG... just start the car, take out the battery and install the new one.

 

I'll raise you an OMG!
Your suggested sequence will mean that the engine is still running when you start to disconnect the battery. That will cause a voltage spike through the alternator that will fry it (actually, the diodes) -- no more alternator. In modern cars with alternators (when was the last time you saw a generator in a car -- maybe mid-1950's?), the battery also serves as a moderator to dampen the voltage spikes caused by an alternator.

 

Assuming that the old battery is good enough to start the car.

Do be extra careful not to let the positive wire touch metal while your two hands are otherwise engaged.

 

So I found one at a local auto parts store -- the kind that plugs into the 12v port and uses a 9v battery for power (the battery will last about 2 hours, long enough...I hope).

On my forester the 12v port is not live when you shut off the engine. So the memory keeper will NOT energize the car's memories (radio, etc.) while you change the battery -- and please don't keep the ignition or accessory mode "ON" to get around this problem because then there will be SO many current drains on your little battery that it will fail in minutes, if not seconds.
Find a better way, maybe through your fuse box.
Personally, I've changed my battery without any memory "doohickey" and I don't remember having lost any settings.

 

... please don't keep the ignition or accessory mode "ON" to get around this problem because then there will be SO many current drains on your little battery that it will fail in minutes...

This is correct! A memory keeper would likely not work via a 12V outlet with the ignition on. These outlets are typically fused at 10 or 15 amps. On my 2019 Forester, with ignition on and engine off the battery current is a little over 20 amps.

 

You don't need to power the whole car to keep the memory, just one small circuit that is easily powered through the OBD-2 port.

 

This is all brand new to me -- haven't had to install a battery for decades (I'm of the generation who had VW Bugs with batteries under the rear seat that would start fires by connecting with the seat springs and/or fall through the rust holes in the floor onto the street.)

Somebody here must know about this stuff, and I'd appreciate some insights. If the car computer doesn't even need a memory keeper, that would be great, but if it does, will what I got do the job? Thanks. (I'll keep hoping that the 50-lb Odyssey battery that the FedEx driver dropped on the concrete floor with a resounding thud is OK -- no damage to the box, nothing visible on the outside of the battery, seems this battery is overbuilt for durability.)

It's a convenience thing ...however, the more electronic computer-influenced geegaws your car has, the more you might consider scoring a memory keeper. Also, the engine management and transmission control computer may be affected if they don't have some kind of holding capacitor to keep their short term memories alive. The inconvenience is they must "relearn" and during that time your car may run and/or shift a little "funny" for a bit. I have a 2011 Foz and swapped in a new battery with nothing untoward happening ...save for the radio and clock losing saved settings and the correct time. If the car has an alarm, if it has a bunch of "bitchin' betties and auto braking ...then I would consider getting a memory keeper. I ended up buying one (I'm a tool junkie) that uses the ODB II port and another 12v battery or another vehicle's ciggie lighter. The BIG factor with any of the 12v-powered setups is your electrical system will be back fed with power from the other 12v source through the OBD II port (or possibly the cigarette lighter/power socket) ...meaning the electrical system is live ...meaning you have 12v and current at the positive battery lead in the vehicle you're swapping out the battery ...meaning you need to make sure the positive (red) battery cable does not touch ground ...lest you end up doing some unintentional arc welding and potentially frying some fuses. I suspect the same is true of the memory keepers powered by the 9v transistor radio battery ...you just won't have the potential for arc welding; best to read the instructions and warnings. And yes, I have a '73 Beetle ...

 

OBD II is the way to go because one terminal is always hot. It takes less than 9v to keep volatile memories energized.

 

A regulated power supply limited to 1 amp keeps all these hazards in check. 1 amp is wholly sufficient to power the system immediately after ignition off and doors closed, and you don't have to wait the 20 minutes or so to full power-down (70 milliamps or less) of all system. And it's totally safe. Short the positive terminal to a fender and you'll hardly notice the spark while your DVM alerts you to the drop in voltage. And even then, the dip rarely goes low enough or long enough to even be felt by the electronics in the vehicle. No need to do any resetting thereafter. Nothing misses a beat.

How you attach it is up to you. I like the alternator + terminal under the red cap on a Subi, as it's up top, easy to get to, and leaves the battery terminals free to 'rubber glove' as I clean the battery tray and hold-downs. OBD port works, but don't blow that little fuse on the +12 terminal. Cigarette terminal only works if it's always alive (most are not). Turning the ignition on to power it up draws a lot more current.

Where did I learn this? From the automotive electronics designers I worked with over my many years in semiconductor chip prototyping. Our lab took in external contract work, and I got to assist automotive, aerospace and all sorts of consumer electronics designers from a broad spectrum of big company names. It's what they do. It's what they tell their fellow automotive people to do. Backup power is the key to logic state stability. Bouncing power when reattaching terminals and the problems it can cause is the most feared event in the minds of many I talked to.

 

A regulated power supply limited to 1 amp keeps all these hazards in check. 1 amp is wholly sufficient to power the system immediately after ignition off and doors closed, and you don't have to wait the 20 minutes or so to full power-down (70 milliamps or less) of all system. And it's totally safe. Short the positive terminal to a fender and you'll hardly notice the spark while your DVM alerts you to the drop in voltage. And even then, the dip rarely goes low enough or long enough to even be felt by the electronics in the vehicle. No need to do any resetting thereafter. Nothing misses a beat.

How you attach it is up to you. I like the alternator + terminal under the red cap on a Subi, as it's up top, easy to get to, and leaves the battery terminals free to 'rubber glove' as I clean the battery tray and hold-downs. OBD port works, but don't blow that little fuse on the +12 terminal. Cigarette terminal only works if it's always alive (most are not). Turning the ignition on to power it up draws a lot more current.

Where did I learn this? From the automotive electronics designers I worked with over my many years in semiconductor chip prototyping. Our lab took in external contract work, and I got to assist automotive, aerospace and all sorts of consumer electronics designers from a broad spectrum of big company names. It's what they do. It's what they tell their fellow automotive people to do. Backup power is the key to logic state stability. Bouncing power when reattaching terminals and the problems it can cause is the most feared event in the minds of many I talked to.

Interesting, though I don't know exactly what you're talking about regarding, well, a lot of it:
1. "regulated power supply limited to 1 amp" -- what would that be? and use it instead of one of those OBD2 memory keepers (it's in the mail on its way to me)
2. "you don't have to wait the 20 minutes or so to full power-down (70 milliamps or less) of all system" -- clueless here
3. "I like the alternator + terminal under the red cap on a Subi" -- this is where you attach the "regulated power supply limited to 1 amp"?
4. "OBD port works, but don't blow that little fuse on the +12 terminal" -- again, clueless -- you're saying a "regulated power supply limited to 1 amp" works better and never misses a beat? and no worries about blowing that little fuse? not that I'd know where that little fuse is...

Along with the normal electronics, my Subie has automatic braking and lane departure assist and adaptive cruise control and god knows what else -- many here who've changed their batteries report no or minimal issues, but that could be specific to the car, even one with the same equipment, so the less I mess with that stuff the better, which is why I guess I could be accused of "overthinking."

I don't know where @WTL purchased their battery, but there was no core charge when I bought one via Amazon. Price was the same as local, that I would have had to pay a core charge, I would have had to drive and pick it up, and hand over the battery that I used for my trade in car to get the core refunded. No advantage there, or the satisfaction of giving Subaru their battery back.

You may also pay tax on the core charge that you do not get refunded. Depending on your state laws.

I bought my Odyssey battery at West Coast Batteries in SoCal, who despite their name have no stores in Oregon or Washington. $308.99, no core charge and free shipping, and they had the batteries in stock. Odyssey told me that the CCA of 675 as labeled on the battery was incorrect -- it's 765, they found the CCA of this battery had been underrated and so they've corrected the label, the battery itself remains the same. I'm told I can return the old battery to AutoZone, don't know if I'll have to pay anything. I would have bought it there but when I asked about Odyssey batteries, the guy said, "Duh, whut?"

 

Watched a youtube video on changing the battery in my 2018 Forester, and for the first time heard about memory keepers. Say what? Seems it's to preserve the car's computer memory settings, of which I guess there are...lots.

So went about looking for one -- some people say you have to plug into the OBD 2 (say what?) and attach to an external power source, like another car battery or a jump starter.

Others say you just need one that plugs into the 12v port and attach a 9v battery to the memory keeper.

And others say you don't need to do any of that, just pull the old battery and pop in the new one, and you don't lose any of those settings. The Forester manual doesn't say anything about it that I could find.

So I found one at a local auto parts store -- the kind that plugs into the 12v port and uses a 9v battery for power (the battery will last about 2 hours, long enough...I hope).

This is all brand new to me -- haven't had to install a battery for decades (I'm of the generation who had VW Bugs with batteries under the rear seat that would start fires by connecting with the seat springs and/or fall through the rust holes in the floor onto the street.)

Somebody here must know about this stuff, and I'd appreciate some insights. If the car computer doesn't even need a memory keeper, that would be great, but if it does, will what I got do the job? Thanks. (I'll keep hoping that the 50-lb Odyssey battery that the FedEx driver dropped on the concrete floor with a resounding thud is OK -- no damage to the box, nothing visible on the outside of the battery, seems this battery is overbuilt for durability.)

A cigarette lighter memory only works with the ignition on. If you disconnect and reconnect the battery with the ignition on, you might fry some of your electronics. As far as the gorillas at FedEx, you are better off going to the store yourself with your old battery. This is the only way to get your core charge refunded.

 

This is the only way to get your core charge refunded.

I don't know where @WTL purchased their battery, but there was no core charge when I bought one via Amazon. Price was the same as local, that I would have had to pay a core charge, I would have had to drive and pick it up, and hand over the battery that I used for my trade in car to get the core refunded. No advantage there, or the satisfaction of giving Subaru their battery back.

You may also pay tax on the core charge that you do not get refunded. Depending on your state laws.

 

Running the engine without the battery may do some damage, it may not. The potential to have a wild voltage spike is certainly there. It is not the best idea. It is an even worse idea to actually reconnect a battery that may not be fully charged, that was sitting on a shelf for a few months. That's where you'll get a much bigger arc than just reconnecting the existing battery.

Ever since there have been ECU's in cars, it has been generally recommended to never disconnect or reconnect the battery with the ignition keyed on. It's the arc that creates voltage spikes well above 100 volts. The only saving grace in most situations is the amperage isn't extreme. But with the alternator being driven, the possibility for a huge surge in amperage is much higher.

The battery is what keeps the voltage stable. The voltage regulator can to some extent, but any surge in demand may create it to bounce between undershooting and overshooting target voltage without the battery there to smooth it out.

I doubt you'll blow any fuses, but there is certainly the potential to blow out some solid state stuff. It would be nice if all it did was blow some fuses, those are cheap. A circuit board, not so much. Good luck buying just the circuit board for any component these days.

 

It's the arc that creates voltage spikes well above 100 volts.

An arc is just current flowing through the air instead of a conductive solid/liquid material. An arc does not in itself create voltage spikes. Any time you connect or disconnect something, or even just flip a mechanical switch, there's an arc.

 

My local battery shop has a small 7 or 8 AH battery they connect to the cars cables using heavy duty crocodile clips.
This maintains power to the cars while they disconnect and replace the main battery.
Simple and safe.

 

trailangel said:
OMG... just start the car, take out the battery and install the new one.

Never, ever do this! Without this load on your alternator, you will fry every fuse and microchip in your car.


SaveShare
OMG...... I have ruined my beloved! I do this all the time......for years. The last 2 times I needed a battery I called AAA auto club to come out and replace my battery... on Suby and Camry........did the Accord myself.
They start the car, take battery out, put new battery in. Never have I had any kind of electrical problem in ANY of my cars.
Over 50 years maintaining my own vehicles, and members of my family.
Don't pull the fire alarm when there isn't any fire!

 

ALL,

This is a reminder of the title of this thread "Installing new battery - do I need a memory keeper?". We're drifting off into various tangents and opinions on what is a safe procdure, etc..........

 

To answer the question.... NO, you do not need a memory keeper.

 

Watched a youtube video on changing the battery in my 2018 Forester, and for the first time heard about memory keepers. Say what? Seems it's to preserve the car's computer memory settings, of which I guess there are...lots.

So went about looking for one -- some people say you have to plug into the OBD 2 (say what?) and attach to an external power source, like another car battery or a jump starter.

Others say you just need one that plugs into the 12v port and attach a 9v battery to the memory keeper.

And others say you don't need to do any of that, just pull the old battery and pop in the new one, and you don't lose any of those settings. The Forester manual doesn't say anything about it that I could find.

So I found one at a local auto parts store -- the kind that plugs into the 12v port and uses a 9v battery for power (the battery will last about 2 hours, long enough...I hope).

This is all brand new to me -- haven't had to install a battery for decades (I'm of the generation who had VW Bugs with batteries under the rear seat that would start fires by connecting with the seat springs and/or fall through the rust holes in the floor onto the street.)

Somebody here must know about this stuff, and I'd appreciate some insights. If the car computer doesn't even need a memory keeper, that would be great, but if it does, will what I got do the job? Thanks. (I'll keep hoping that the 50-lb Odyssey battery that the FedEx driver dropped on the concrete floor with a resounding thud is OK -- no damage to the box, nothing visible on the outside of the battery, seems this battery is overbuilt for durability.)

I seriously doubt the cigar lighter type 12V ports are relay switched. The way to determine this is to insert a plug into any of the 12V ports ports with the ignition off then measure the voltage. The least expensive way to protect these ports is a fuse since a relay or MOSFET requires bias voltage to engage or turn it on. That circuit would also be fused as well resulting in unnecessary series fuses. I have seen a wiring diagram which is the way to determine the exact connection of these ports to one of the common 12V buss lines.