symptoms of dying 12V battery, but battery voltage is healthy

Check for codes. You may have a problem with your braking system.

 

possibly. what is the voltage in the morning before starting the car?

 

What did you use to measure the voltage, a multi meter with the car off, or something in the car's displays? The car's display may be biased. Also, how old is this battery? It's original?

The smoking gun is the 3 week hiatus. Maybe try disconnecting the 12 volt negative lead, wait a minute or two, then reconnect, then hook up a smart charger, something in the 3~4 amp range, and capable of running a charging regiment. Just let it run through it's cycle, could take 8 hours or so. Then test drive and see what happens. If the warnings come back, get a dealership on it I guess.

Even with decent voltage, it may be messed up. Something like prosumer level Solar BA5 would make better assesment, check both voltage and Cold Cranking Amps. Most automotive retailers selling batteries would have a pro-level version of such a tester, would test for free. Or dealership, for a nominal charge.

 

Here is a relatively easy way to test your battery with a multimeter. Your Prius does not have a typical starter but this test will work none the less.

 

Unplug the 12v + battery post then the -, wait for 5 minutes then plug + first and - last. Start car and see if the code slip indicator dissapear. If slip indicator comes back, might be bad 12v battery. Take it to an auto part store that will do a free load test on the battery. Batteries can have a nominal voltage but when its under a load, voltage will plummet and that means curtains for the 12v battery.

Also depends on how long you drove the prius around right after jumping it from 3 weeks of non-operation, 10 minutes of driving won't recharge the 12v battery to get back to normal charged state.

 

How old is the 12v battery?

My oem battery died at 4 years and still measured 12.7v, but the doors wouldn't even unlock and dash lights died as well, only an exclamation point in a triangle, if I recall correctly.

Posted via the PriusChat mobile app.

 

How old is the 12v battery?

My oem battery died at 4 years and still measured 12.7v, but the doors wouldn't even unlock dash lights died as well, only an exclamation point in a triangle, if I recall correctly.

Posted via the PriusChat mobile app.

 

I understand the Prius doesn't use the amperage because it doesn't have a starter. But you can't JUST rely on voltage.
That's just the start. You need to check amperage. Turn the headlamp on hi beams, then check the voltage.
That's a minor load test. You could turn ALL the 12v items on, dome lights, radio, etc. which provides more of a load on
the 12v battery(without turn the car on) and then see what the voltage is.
A standard fuel injected car needs a minimum of 9.6 volts(like the video above) to run the computer to run the fuel
injection system WHILE the starter is cranking, or the car won't start.
The Prius doesn't use ColdCrankingAmps, but still needs enough amperage to keep the voltage up.
Is that not correct???

 

Yes, I think your post is absolutely correct.

Except for "But you can't JUST rely on voltage."

You absolutely CAN rely on voltage alone.......IF you test it under the right conditions AND know what the result means......just like you said in your post.

 

One of my favorite puzzles (after we figured it out, anyway) was a friend's Ford Galaxie that seemed just fine when you walked up to it, unlocked the doors, tried the lights, all fine, no sign of battery trouble, so you'd turn the key to start the car, and all the lights went out. And then they'd stay out ... no power anywhere in the car ... for two or three minutes ... and then blip! all come back on again, full brightness.

It was just like some giant self-reset circuit breaker was in the main battery cable. Only that wasn't a thing....

Battery was fine, one of the clamp-to-post connections was just so marginal that it could conduct plenty of current for the lights and miscellaneous stuff, with no obvious sign of voltage drop.

Turn the key to start, and that amount of current through the marginal connection would heat up the clamp ... until it expanded around the battery post ... and broke what marginal connection there was.

Then over the next two or three minutes, it cooled off, contracted, and made contact again.

That was easiest to catch by putting the meter leads on the cable clamps, rather than directly on the battery posts. (I bet it would also have been dramatically obvious on an IR imager, but I never had my hands on one of those until many years later.)

So yes, it can pay to identify whatever assumptions you might be making, and get some measurements of those, too. They might just confirm your assumptions 19 times out of 20, but that 20th time will seem very mysterious until you do.

-Chap

 

I had a glass fuse like that! What a pain! It was on my 78 Corolla, alternator circuit. It kept going on and off.
I cleaned all the connectors related to the charging system, even the fuse. I even pulled it out and checked it.
I decided to switch fuses with another circuit of the same amperage. Problem went away.
Turns out the had a cold solder inside the metal part.
Since then, that is one of the first things I do, replace the fuse with a KNOWN good working one!

 

I've found that there is an audible sound the car makes when the 12V is weak. You've probably heard a small pump running under the hood right after shutting the car off. When that pump starts to sound (Dating myself) like an old 56K modem trying to connect you have a dying 12V battery.

 

I had a 1200 baud modem!

 

110 baud

 

My brother used one of the first ones. SUPER slow. I don't remember what it was...

 

Probably a Commadore “Vic 20”. Still have one in my garage.

 

I used to be able to whistle the right tone to make a modem say "CONNECT 1200" ....

 

a closet phreaker?
EDIT: Showing my age

 

I can still do 1600 for the army tone for the equipment I can't remember the name of..

 

It was really handy for testing an outward-dialing modem bank. I could just sit at my terminal and connect to each one in turn and have it dial the phone at my desk, pick up the phone, whistle at it, see it say CONNECT 1200, hang up, and move on to the next one.

Others in the room weren't always sure what to make of it ....

-Chap