12V Battery Replacement Recommendation

It’s 2025, but just wanted to let anyone who might need it, Amazon has OBDII memory savers that hook into OBDII and a 9v transistor battery for ~17 dollars. Search using this on Amazon:
9V Battery Powered Memory Saver for Car Battery Fit for All OBD ll 16-Pin Interface

 

So you attach this device to the obd2 port while you are changing out the 12V battery? Would it not create excessive charge briefly when both the battery and this device are connected? Is that ok?

 

It doesn't: voltage sources in parallel do not add. 12 volts ∥ 12 volts = 12 volts.

 

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Speaking of 12V chargers, has anyone used this Bosch charger?

 

Mendel Leisk has experience using the obd2 port for memory saving. I’m new to this forum and not sure how to contact him. I haven’t tried (or purchased) it yet. The amazon page has user reviews on using the product I’m looking at, which may also be a good source.

 

Yeah I posted this the other day.

That said, if I’m going to take brake calipers off the rotors, first thing I do is disconnect the 12 volt battery’s negative cable, without using a memory saver. It’s no big deal. I don’t really care about radio presets though.

 

To me, radio preset loss is a trivial side effect of disconnecting the battery. One annoying side effect is the resetting of calendar date in the display dash. I still don't know what the thinking was behind it. Perhaps the most important items in memory are learned parameters which can impact gas mileage. Still, it's a no brainer that one should disconnect the battery (and not use any memory saver tricks) when repairing brakes.

 

You have to disconnect the battery to replace brake pads? Is it because of an electric pump for the brake booster?

 

Mostly, yes. There’s been multiple reports here, someone has the caliper off the rotor, opens drivers door inadvertently, system pressurizes, and piston pushes out of caliper.

also, if you’ve pushed/screwed back caliper pistons to accommodate new pads, there’s a chance that a “sentient” brake system will detect excessive brake pedal travel, throw code.

battery disconnect is a blunt tactic for DIY’rs, just “better safe than sorry”, but it works.

 

Thanks I had to ask. I've replaced a fair number of pads and rotors on 'regular' cars over the years, and have never disconnected the battery. Here's hoping the brakes last a long time on my '26. There's a lot to learn.

 

Toyota USA “seems” to be recommending a tri-yearly or 30k mile brake inspection. It’s easy to overlook, due to the format of the Warranty and Maintenance Booklet, doubly so due to vague wording. Usually the pages say to “visually” inspect brakes (every 5k miles, presumably during tire rotation), but at 30k, 60k and so-on miles, the visual inspection statement is omitted, and a statement to check calipers and rotors (paraphrasing, it’s something thus) is added.

 

I imagine that you can also send some commands through Techstream to let the ECU know that you are working on brakes. Would be curious to read about that procedure.

 

I generally don't on my Prius, but I do pay a bit of attention to timing.

The brake system does have a pressure pump, which runs from time to time as needed to keep fluid at a high pressure in the accumulator, which is a pressure vessel under the hood for supplying pressurized fluid when needed.

Note that running the pump and pressurizing the accumulator does not apply pressure at the brakes. The valves in the actuator are responsible for opening and sending pressure to the brakes, only when needed to slow the car.

Any pressure at the brakes that you could observe just because the pump runs would mean some valve(s) leaking in the actuator to constantly apply the brakes, which would be a serious problem. It would suck to find out about such a problem because pistons popped out during your brake job, but chances are that wouldn't be how you'd find out; you would already have noticed you were driving around with brakes on all the time.

The timing that I do pay attention to is the timing of the brake system self-test that always gets conducted 90 seconds after power off. If this isn't familiar to you, it's easy to sit in the car with a stopwatch (or the stopwatch feature on your phone), turn the car off, and wait 90 seconds, when you will notice the sounds of valves clicking and of brake pressure being applied and released. Then you'll know how to recognize the brake self-test when it happens.

That self-test really does send pressure to the brakes, and so it really will pop pistons out if it happens while things are out of place. That's why I make sure to wait until it's already happened before I take anything apart.

There is a mode (or more than one mode) called "ECB Invalid" mode (ECB is Electronically Controlled Brakes), which you can get into using a scan tool, or with a non-scantool jumper wire dance.

I say maybe more than one mode, because there are signs the effects might not be exactly the same when you enter it with a scan tool as when you enter it with the jumper dance.

I haven't used that mode much. One time I did try it, I ended up having to learn what the C1451 code is all about.

 

Would that be the cause of the dip in voltage right after turnoff?

 

POST vs POST: Power-Off Self-Test (as opposed to Power-On Self-Test)