12 volt battery failing to start the car

Wait a minute,,,
Is the Owner's Manual this cryptic in other areas? That attachment makes no sense to the average dummy.
WTH is "20hr rate is low".....

Why can't you just drive it like a normal person and plug it in at home and forget about it like a normal PHEV or BEV owner?

 

Wasn’t joking that much about the Twilight Zone.
The part in red, I said that in my post, increases the 12 v discharge rate if cable is left attached. How much does it increase, like 1% or 10% was my question. These are engineers writing this, .001% is an increase.
I never leave mine plugged in not charging, maybe ten minutes a couple times over six months.
Going to check the charging of the 12 v myself. Too much reading not enough action.
I thought the part about starting the engine every 2-3 months, letting it run till it shuts off, then turn power off was strange. It seems the traction battery can get low too, and this cures it. So it’s not good to leave the traction battery at 0% then go on vaca for 10 weeks? So what do we leave it at, 20%? It’s the Zone.

 

While charging, the plug does supply power to the 12V system. When not charging, the cord is not energized, so no power to anything. That is how all EVSEs work. They don't allow electricity flow to the car until communication is established and safety checks performed. Then they cut the power when the car says it no longer needs it.

The monitor systems in the car stay on with the plug in. That is an additional draw over what an unplugged car sees. Likely isn't an issue with a healthy battery. A small capacity 12V is more likely to end up in the unhealthy area.

Some EVs do periodically power up, either by plug or traction battery, to maintain the 12V. Others do not, or the process isn't enough over time.

 

Any idea how an owner would know "if the 20 hour rate capacity is low"? Does this correlate to a particular voltage reading? And how low is "low"?

I suspect that this is something that requires some sort of equipment that tests the battery under load and that's something that is more likely to be checked after there has already been a problem.

For what it's worth, apparently that comment only appears in the Prime manual. I couldn't find it in the manual for my LE. So perhaps the Prime puts additional stress on the 12v battery.

 

Just curious, have you confirmed that it's at 100% by measuring the voltage before you go into Ready mode? Or do you just assume it's at 100% because you haven't had any issues?

Lot's of anecdotal comments, which are valid, but I keep hoping that those who have reported issues with their Gen 5s will post follow ups with additional info. Perhaps they don't check the forum very often.

I seem to be the only one here who has been actively monitoring voltage using a meter that plugs into the lighter socket, which is very inexpensive.

https://www.ebay.com/itm/284570867184?hash=item4241bed5f0:g:sF0AAOSwo11huypU&amdata=enc%3AAQAIAAAA8E0rDzzd6%2Fi0yqAWBQgXa4mev2Lf0tUuH8dMLMCig4VhH0EtePBgT42v4p5fD6oEBCQfdnzjnljVgTvyQlKT9ooDNBF3K82Zbmy9u0avN2S9FuAM2Iq%2F1SLp9w3FsiBRFv2L0rwMtuTVhZyteUYNRUCI8rwSXxkwc43B90%2BoliTDRB2qnd4a3U4ZrzW4bW9WG%2BuuK7jHPGUn041FrEljgAKBDNOmUpx4qAlFHS098WwqGVlq22IYNvJPOHUI65dAnKSdgIMqWwRJWjV0y9CDtlNO9%2B2D58ZHsHpTiS5IFqwN1kNs5MS%2F8OXjCFnVrr9jiQ%3D%3D%7Ctkp%3ABk9SR7DRvoXZYg

As I stated earlier, when I get into the car I turn on ACC to check voltage before the battery is being charged. I typically get a reading of ~11.6v (20%) and within a few seconds it jumps up to 11.9v (40%) or 12v (50%). Then I go into Ready mode and the voltage jumps, typically to ~14.2v, which indicates that it's being charged. After driving a while it will eventually read 12.7 to 12.8v (100%) but the next day the same pattern repeats.

I did hook up a solar charger but the car is parked under a carport so it only gets direct sun for an hour or two at this time of year and ambient light most of the time. Even then, it has LEDs that indicate that it's getting power and is sending at least a bit of a charge to the battery. When I go shopping and I'm in a store for a while it gets direct sun too but not for extended periods of time.

So it seems that the SOC (state of charge), even with the solar charger, drops from 100% to 40% or 50% within a day or two.

 

Are you sure other makes are not the same? I know in the Kia Niro EV forum, seems it’s the same thing. I was looking at one instead of the Prime so looked up things people were having troubles with.
You already stated you don’t want a Prime anyway, and this is just for a friend, not you, right? So tell them not recommended. One less in line to get one. Maybe they can ask someone else.
Actually it’s the same for all cars, just some charge up faster and have larger 12 v batteries. I trickle charge my 1996 Toyota truck quite often. 1998 Chrysler minivan, in the manual states 12 v shouldn’t be left more than 20 days due to drain. Never used to care either, but learned more that if it starts is not the only important thing. $200 battery life is also important.
Then there is the fact 100,000’s of small car chargers are sold everywhere and lots of them. Someone normal must be buying some of them. Then there is calling AAA for a jump or new battery, which avoids all thinking.

 

Ev’s have had more 12 volt problems than gassers, from what I’ve read.
Bolt recommends leaving it plugged in all the time, or put a maintainer on it

 

The Bolt is one that will power up to help maintain the 12V. According to the manual.

 

That doesn't sound right at all. If the SOC dropped 50% in a day, the battery would die in two days. As I said, I left the car undriven for more than six weeks with no issues. I have an active Toyota Connect subscription as well. Your results don't agree with @Salamander_King's results.

Perhaps your SOC is always remaining around 50% because you are not driving the car for long distances? Also, I would ignore the transient behavior of battery voltage like it changing within seconds.

 

I am sure the AC-charging cable results in a significant current draw from the 12-V battery to operate the charging system and vehicle communication systems. I wouldn't leave it plugged in. In fact, that could be the reason why some Prius Prime owners reported a dead 12-V battery.

I left my PHEV battery at 24% on MFD—specifically adjusting it so to limit capacity degradation—and the 12-V battery probably at or near 100% SOC with the car undriven for more than six weeks with an active Toyota Connect subscription and of course the AC-charging cable unplugged. Temperatures were warm with the car garaged. Guess what the PHEV battery SOC was when I returned: It was still 24%. There were no issues with the 12-V battery either.

 

That is the 12-V battery energy capacity in ampère–hours (Ah) @ 20-hour (hr) discharge (equivalently the reserve capacity in minutes @ 25-ampère (A) current drain). It is saying that if you replace the OEM battery, replace it with one with the same or higher specs—or else.

 

Toyota engineers know what they are doing, and this is probably deliberately by design—e.g., to ensure safety. There is no reason to keep the AC-charging cable plugged in when the car is not in use for more than a day.

You shouldn't even leave the charging cable plugged in to your cell phone either, as keeping the battery at 100% SOC greatly degrades its capacity over time.

 

When you call AAA that when you know the battery

Gassers are not usually left ignition on long, and it was a good system for keeping the battery charged with the generator pumping out 50 amps or whatever. I used to watch my ammeter and it told you pretty much your battery was full or not with a glance. As it charged up, the amps no longer went positive. It took no brain. Sitting at a light with things on, see the negative amps. No brain required. This is why I still can’t answer my cell phone correctly every time, I need simplicity. So they took ammeters out of cars and now we have all this talking. No reason why the Prius can’t have an ammeter on the 12 volt, is there?

 

Not only an ammeter but Prius Prime has a dedicated sensor for the 12-V battery to measure its voltage, current, temperature, SOC, SOF, and SOH and do a self-diagnosis to optimize its charging current to extend its life.

The battery characteristic (battery internal resistance) of taking in current for charging varies in accordance
with battery electrolyte temperature. If the battery electrolyte temperature is too low or too high, the battery
will degrade more quickly, resulting in premature failure.

(a) The battery sensor (battery state sensor assembly) installed to the negative (-) auxiliary battery terminal
calculates the current, voltage, battery temperature, SOC (battery charging percentage), SOH (battery
degradation percentage), SOF (starting performance) and self-diagnosis result and sends these signals to the
hybrid vehicle control ECU via LIN communication.

(b) To detect the current, a shunt resistor installed inside the battery sensor (battery state sensor assembly) is
used to convert and calculate the voltage generated in the shunt resistor due to the battery charge and
discharge current.

(c) The battery temperature is calculated from the resistance value of the thermistor built in the battery sensor
(battery state sensor assembly).

 

only when plugged in, and it's recommended

 

I want to see the ammeter as I drive. I’ll decide what to do with the info. How do I have that?
The manual also says the evse has a lifespan based on use. A light will come on when it is used up. I never heard of anything like that.
On my Volt the battery was kept well. Whatever they do, they do it well. Never charged it in three years and the couple times I measured it, it was well charged. Driving exactly like I do now.
Yesterday my evse was unplugged. I think someone was going to steal it. Of course the other end is locked. $250 or so on ebay, waiting to be grabbed. Or someone wants a free evse just because.
Those who have an LE there is a hole in the handle for a small padlock. I did this on my LE.

 

Where did this idea come from?
I have been driving PHEV and BEV's since 2013.
Yes.
There is a very good reason to keep your PHEV or BEV plugged in.

Well engineered PHEV's and BEV's have an active TMS to keep the HV pack in a happy temp range.
It's called a Thermal Management System.
What does the Prime have for TMS?

Unless you live in paradise, a Li-ion pack should have its temp controlled, even when just parked.
Would you agree?

 

I’m thinking the manual was writing about running the gas engine every 2-3 months to exercise it till it shuts off. First time I read it had to read again because it reads like it is the battery getting low. Maybe it is translators and proof readers getting things mixed up. Anyway you didn’t make it to 2-3 months and are arguing with the manual, not me. I already assumed the main battery wouldn’t discharge so fast just sitting. I have power tools that sit for years and the battery level bar is at the same place. They even ship them with like one bar and a year or two or three later someone buys it and it’s still at one bar. I’m voting for manual writing is off. I think the 2-3 months is to work and lubricate the engine. Start, let engine run till it turns off, then push off button sounds like engine related. Or the engine runs and charges the battery is more how it reads, so who knows.

 

This is not the correct interpretation at all.

What Toyota is worried about is the people who never charge their PHEV battery and only do HEV driving. Add instances of HEV-reserve depletion after a certain trip and then leaving the car undriven for several months. This could potentially result in a dead PHEV battery and a bricked car that requires a PHEV-battery replacement. Toyota is instructing so that you at least replenish the HEV reserve by starting the car and then waiting until the engine stops when the HEV reserve is full before you leave the car in storage.