Battery change memory savers

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I have a new "memory saver" that attaches a 12V power source (e.g. Spare battery) to the car's OBDII port during a battery change to save radio presets, PCM "learning" and the like.

This seemed like a "no-brainer" and a smart thing to do but I see conflicting advice on, you guessed it, the Internet: some sources say it's prudent and almost essential but other say it's dangerous.

What's been the exprience here? Thanks.
 
I tried using a saver on my lexus OBD port and lost everything this way.

Going forward I will use one of my smart chargers with a "maintain mode" for this connected direct to the battery leads.


UD
 
depends on the vehicle and you have to be careful. ODB ports are only spec'd for 4 amps officially, but it depends on what fuse they're running off. Interior lights, auto lamps/DRL, fancy radio head units and the like can draw quite a bit of power

You have to plug it in and keep the doors closed to ensure the vehicle won't draw too much power. If you accidentally open the door with the battery disconnected, there's a small chance you could blow a fuse and have to go hunting for it.

Typically, when I have the time or it's important to not lose settings like security codes, I will use a small 12V SLA battery with test leads to battery lugs or fuse panel under the hood.

With proper precautions taken, they're very convenient to have around and if it has a 2 pin sae connector, it can be used with a bunch of different battery maintainers and low amperage chargers.

Some of the Noco chargers have a 12V 3-5A maintain/supply mode that works well for this.
 
The conventional device uses 9V battery hooked through the lighter socket.

A 9V battery doesn't need a fuse. It's so weak it can't put out enough current for a dome lamp, let alone blow the typical 15 amp fuse for the lighter socket.

You don't see these devices much any more. Most settings are stored in non-volatile memory, and a 9V battery isn't powerful enough to run the ECUs in not-quite-asleep mode.

I wouldn't use a smart charger, or a really dumb one. A smart charger will shut off when it doesn't detect a battery, and typically produces high frequency noise on the output that may not properly power ECUs. A dumb charger may output a high voltage with no load, and may be essentially unfiltered 60 Hz pulses.
 
Originally Posted By: HorseThief
depends on the vehicle and you have to be careful. ODB ports are only spec'd for 4 amps officially, but it depends on what fuse they're running off. Interior lights, auto lamps/DRL, fancy radio head units and the like can draw quite a bit of power

You have to plug it in and keep the doors closed to ensure the vehicle won't draw too much power. If you accidentally open the door with the battery disconnected, there's a small chance you could blow a fuse and have to go hunting for it.

Typically, when I have the time or it's important to not lose settings like security codes, I will use a small 12V SLA battery with test leads to battery lugs or fuse panel under the hood.

With proper precautions taken, they're very convenient to have around and if it has a 2 pin sae connector, it can be used with a bunch of different battery maintainers and low amperage chargers.

Some of the Noco chargers have a 12V 3-5A maintain/supply mode that works well for this.


Just to be sure I understand, you'd rather use essentially a spare 12V lead-acid battery with jumper cables attached to the positive and negative battery cables than going through the OBDII port? Thanks.
 
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I just use my little jump starter at the battery cable terminals. Switched out 3 vehicle batteries recently, no issues.
 
I change a lot of batteries on a lot of cars at work (auto parts store) and we never bother with the stupid obd2 memory saver gizmo that corporate tells us to use... never any problems. most cars, especially newer toyotas, stall right away the first time it gets started after a battery replacement since it hasn't learned idle but on the second start it's all good.
 
For memory saving, I use a small lithium-ion jump starter plugged into the DC socket, with a modified cable, EC5 connector and a fused plug.
Then I'd turn on the ignition to connect up the circuit, before replacing battery.

I tried to connect at the battery terminal, but sometimes, the clip would slipped off or get knocked off by my changing of the battery.

The DC socket way is more reliable, but have to watch out for high current drain from devices, such as hazard lights, and DRL lights that won't go off.
 
I have used the 9 volt in the cigarette lighter for decades and have 0 issues. It's fused and it has a diode.
Just be sure to use it in a port that isn't wired to shut-off with the key.
 
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Originally Posted By: Eddie
I just write down my radio stations etc and it takes me about 2 minutes to re-install. No mess-no foul and good to go. Ed
I just changed the battery in the Cobalt, no maintainer, and interestingly enough, the radio retained all the station settings, but the clock needed to be reset.

I did take pictures on my phone of all 5 preset banks just in case, but didn't need them.
 
Originally Posted By: vwmaniaman
+1 on the jump starter


Same here, I leave a jump starter with the spring clamps attached to the battery leads and a ground somewhere. It is a little tougher to deal with since the clamps can slip off while installing the new battery, but I manage considering how infrequently I have to do this procedure.
 
Originally Posted By: edwardh1
odd that the car maker does not cover this in the owners manual


Shop manual yes, owner's manual no. Most shops will use a trickle charger or jump box connected directly to the battery when doing any PCM updates or module flashes per almost every FSM.
 
Originally Posted By: Danh
Originally Posted By: HorseThief
depends on the vehicle and you have to be careful. ODB ports are only spec'd for 4 amps officially, but it depends on what fuse they're running off. Interior lights, auto lamps/DRL, fancy radio head units and the like can draw quite a bit of power

You have to plug it in and keep the doors closed to ensure the vehicle won't draw too much power. If you accidentally open the door with the battery disconnected, there's a small chance you could blow a fuse and have to go hunting for it.

Typically, when I have the time or it's important to not lose settings like security codes, I will use a small 12V SLA battery with test leads to battery lugs or fuse panel under the hood.

With proper precautions taken, they're very convenient to have around and if it has a 2 pin sae connector, it can be used with a bunch of different battery maintainers and low amperage chargers.

Some of the Noco chargers have a 12V 3-5A maintain/supply mode that works well for this.


Just to be sure I understand, you'd rather use essentially a spare 12V lead-acid battery with jumper cables attached to the positive and negative battery cables than going through the OBDII port? Thanks.


No - I would love to go through the ODB port, it's just that I won't do it with a customer standing by. I don't want them opening a door or turning anything on (and no - people don't listen when you tell them not to do something) On my own vehicle, that's a different story.

Otherwise, I should clarify - not jumper cables, jumper wires or test leads. 18-16AWG wire with large alligator clips. Aside from GM vehicles where the power distribution panel is mounted on the battery cover, it works well and stays out of the way.
 
Also, to be clear - I don't use a car battery. I use a 5 amp-hour sealed lead acid battery. They're about the volume of a softball, but square. Commonly used for trailer brakes, burglar/fire alarm panel backups, deer feeders, garage door motor backups, etc.
 
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Originally Posted By: edwardh1
odd that the car maker does not cover this in the owners manual


They don't want to admit that their own cars stink at relearning or getting their I/M monitors in order.

I have a little motorcycle battery that backfeeds the OBDII port. Never a problem. One shound ensure the bare positive terminal doesn't get grounded in the process though. Wrapping in a shop rag is fine. Same when changing a starter/alternator.
 
Originally Posted By: HorseThief
Also, to be clear - I don't use a car battery. I use a 5 amp-hour sealed lead acid battery. They're about the volume of a softball, but square. Commonly used for trailer brakes, burglar/fire alarm panel backups, deer feeders, garage door motor backups, etc.


Thanks for the advice. Very helpful and much appreciated.
 
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