12V Memory Saver

you can't damage the computers by changing the 12v

 

I'm not aware of any damage from simply disconnecting the 12V battery, only loss of non-essential computer memory values.

As a "memory saver" procedure, some of us just replaced the battery while the car was running, in Ready mode. Once in Ready, the car (at least numerous Prius models, I don't know about every single one of them) will continue operating without a 12V battery in place. I also turned on the headlights to ensure the HV --> 12V inverter would have a minimum load to keep in regulation, but don't know this to be necessary at all. There are many other loads on the 12V bus that may well cover this.

Some less adventuresome owners, wanting a more cautious approach, have instead left the car turned off and simply attached a battery jump-start box somewhere to the 12V bus -- at the underhood jump connections of Gen2-3 models, which your Gen4 probably lacks. This will provide enough power to maintain computer memories.

I would not hook up an old-fashioned battery charger as a memory saver. Without the battery present, some will drive a too-high voltage. Newer better designs might be better behaved, but I don't know which ones they are, only that my old dumb charger contains no protection.

 

I have paralleled a second 12v battery at the front jump points prior to replacement of a Prius aux battery with no loss of current data. However, I usually just disconnect without concern. I only noticed the radio restarts after a power cycle. All the presets remained as did all of the easily observable settings throughout the vehicle.

Modern ecus save most data in non-volatile memory. There are many procedures in the repair manual requiring negative cable disconnects prior to removing some piece of electronics without any corresponding reference to using a memory saver. This is to prevent accidental shorting of exposed pins. The most reassuring aspect of the Prius electrical design are the many cases of reversed battery or jumper cable polarities that are resolved by replacement of fuses and fusible links.

 

12V doesn't normally shock people to death, or even give a noticeable sting. Though a long-ago coworker got a very nasty burn when his wedding ring was briefly stuck between terminals of a starter.

Gen3 and earlier Prii were better setup up for connecting a jump pack at one point while changing the battery at another. But I had to be sure to not allow the positive cable terminal to hit any ground point, so I shoved it inside a work glove.

Lacking a separate jump terminal, Gen4 will be a bit more tricky to do this without inadvertently losing the connection.

 

Be aware that a small OBD2 memory saver may not have enough current output capability to operate cabin lights or other accessories that may be on while the battery is being swapped.

 

There are only a few items that have to be re-initialized when the auxiliary (12-volt) battery is disconnected and reconnected, and in my opinion, connecting an extraneous device is more likely to cause a problem than prevent one.

Just do the battery removal and installation procedures as written in the Repair Manual (more info).

 

The 200V should be extremely well contained and protected from you, and from ordinary mechanics, and from first responders. And it should have GFCI protection too.

And as others have pointed out, there really isn't that much memory lost if you forego all this and just skip all this 12V-support effort. Nothing essential.

 

in 17 years on priuschat, i don't recall anyone damaging an ecu by changing the 12v. some have used memory savers, but i would say most have not.
some lose their window preset, others radio presets.
i did mine 2 years ago and lost my trip meter

 

Every time I do brake work I purposefully disconnect the 12 volt. Subsequent start ups have a few minor hick ups. Typically widow auto-up is ok, but radio presets and trip meters are gone. First start up, the start button is a little quirky, and I’ve noticed the engine does some sort of rev up (recalibrating?), for 2~3 start ups.

If you’re mothballing a car, it’s a common strategy to disconnect the 12 volt, saves it from being run down by the cars constant background demands.

When I do use a memory saver, it’s a Clore JNC660 jump pack with a Solar OBDII Memory Saver Cable.

The notion that the car’s electronics will implode with battery disconnect? Reminds me of this movie:

Happy as Lazzaro - Wikipedia

 

Yes, indeed it should......unless you make a mistake.

 

You shouldn't have any problem with a simple "disconnect and replace" on the 12v aux. battery. I've had no problems (yet) with my 12v on my late 2017 Prius 2, although I monitor it with a Scangage. My earlier 2008 Gen 2, would on a handful of times exhibit some strange behavior like abnormal running of the brake system boost pump. Disconnecting the 12v, waiting a few minutes then reconnecting fixed it. No such problems with the gen 4.

 

Trip A and B only

 

YMMV. I have never lost anything but the time on my clock on my 2016. Replaced the battery, had multiple upgrades that have had the battery disconnected for hours at a time. My "B" tripmeter is my lifetime indicator and has never been reset.