Okay. Who HASN'T had a 12V battery issue with their 2023-24 Prime?

I don't believe a 2 amp smart charger would be enough to keep a car battery maintained.

 

Mmm, think it would be, just a little poky, but ok. The 0.8 amp chargers might be borderline.

 

It was a '92 T-Bird, which had practically no parasitic drain. It was to guard against internal battery discharge, which was always a given over the winter months. 2 amps was plenty to compensate for that, but the constant charging caused all the electrolyte to boil away, leaving the plates sulfated and shorted out. (Or so I assumed, not being a battery chemistry expert)

 

Yeah a charger that just keeps going full tilt is old-school, cannot be left on constantly. I’m using a CTEK 4.3 (pretty much ‘round the clock), but they’ve got pricey. Nocco’s popular I think, more available and cheaper.

 

It's what my charger on the auto setting drops to when the battery is fully charged. 2 amps is plenty for a float charge.

 

NOCO Genius 10

Any of the Genius models should do the same job, I think.

 

mine is only one amp and worked fine on my prius and bolt for months at a time in winter temps.

 

So far, no issues whatsoever, BUT I plan to upgrade to Ohmmu battery in the future.
Sadly, LifePO4 for car batteries are incredibly rare to find in EU, so I guess I will have to endure the usual route of international shipping, import duties and VAT and all that "good" stuff.

 

LFP batteries are not compatible with the Gen 4 and Gen 5 Prius/Prius Prime due to the presence of a lead–acid-battery sensor, and even if they worked, you would see no benefit over a lead–acid battery, as there is no 12-V fast charging in Gen 4 and Gen 5 Prius/Prius Prime. You would still have the same dead-12-V-battery problem as a result if the car is driven in mostly short trips and/or infrequently.

 

I made a recent trip and over 140 miles mostly freeway, I arrived with 61% soc. Very little charging going on the whole trip. Coming back 140 miles, same thing. Perplexing. It goes under 13 volts, stays there, no charging. I don’t remember what soc was to start with, but it was more.
Car starts fine etc. Car starts fine is fine to notice, but maybe the battery is not so fine?

 

Your battery is quite old, right? Perhaps it has degraded?

Also, where do you get the 61% from? The voltage vs. SOC data is all over the place if you Google it. Some say 12.2 V is 60%, others 12.4 V, and yet some others a different value.

 

About one year old. The soc is from the battery monitor and doesn’t change with voltage. Charging only happens above 13 v. Pretty much at 1 am every night there is downward spike in the voltage. The monitor records up to seven days. A battery load test showed battery ok. I don’t know how to test the sensor. Maybe disconnecting the battery will reset the ecu. I’ll try that some day.
I probably could drive around with no battery start problems. But the battery is still not optimal.

 

Do you have a good multimeter? What is your open-circuit voltage? If you can't measure the open-circuit voltage, a low-load voltage measured at a current of less than 0.45 A should be sufficient. If it is about 12.8 V, then you have a fully charged battery. Note that immediately after charging, the voltage could be higher; so, wait for about an hour after the car is driven or the battery is charged from a charger.

Note that according to Exide, the open-circuit voltage at 100% SOC is 12.96 V (2.16 V per cell) or perhaps 12.84 V, but this seems to be the value for an AGM battery. The open-circuit voltage at 100% SOC for a flooded-cell battery is probably more like 12.64 V.

https://exide.sk/asset/uploads/na%20stiahnutie/NEW_Exide_Edition5_TechnicalGuid.pdf

The following information for AGM and flooded-cell seems reliable:



Lead–acid-battery voltage chart

Moreover, I probably wouldn't want to use an AGM battery in Gen 4/Gen 5 Prius/Prius Prime because the voltage-vs.-SOC characteristics would confuse the battery sensor, especially at a higher SOC.

 

Good info. The battery monitor has round the clock voltages, and stores them up to five days. I wired mine now so the negative lead goes to a body ground. There is a ground screw at the washer bottle.
I do have a multimeter. One of these days I will measure the monitor draw as the meter has a milliamp scale. On my truck it seems the monitor does little to drain the battery. I watch the battery on the truck too.

 

It turns out that the open-circuit voltage also depends on the acid concentration, in addition to the SOC. That's why AGM has a higher open-circuit voltage, as it has a more concentrated acid.

 

THB, I like the chemistry, providing better reliability and a small weight saving.
I will try to post URL to the product, if I am reading it correctly it should be compatible.
12V Lithium Battery for Toyota Prius | ohmmu.com

 

Those LFP car batteries have a built-in battery-management system (BMS), which controls the current, voltage, etc. They could work in an older car, but the BMS would conflict with the battery sensor in Gen 4/Gen 5 Prius/Prius Prime. You would very likely get an error code and the check-engine light come on. Moreover, you would really see no benefit from an LFP battery, as there is no fast 12-V charging in the Prius.

Likewise, the different voltage-vs.-SOC characteristics of an AGM battery would confuse the battery sensor designed for a flooded-cell battery in Gen 4/Gen 5, and you would experience undesired behavior.

The long story short, only use the type of the battery that came with the car. This means, for the Gen 4/Gen 5 Prius/Prius Prime, the only allowed battery type is a flooded-cell battery. Use a good centrally vented calcium flooded-cell battery (central venting not required for Gen 4), and don't lose sleep over it.

 

The battery monitor soc and voltage are independent readings, and the monitor is hooked up to the battery like a multimeter would be. What is really nice is the battery voltage can be read without a lot of guess work. There is a graph live, and saves it's data for five days. No need to open hood, etc, just stand a few feet way. I may look into getting a more expensive one. What am I missing here?

 

In your simple battery monitor, which is probably only a voltage sensor, the SOC is probably looked up from an SOC-vs.-voltage table like the one I posted above. So, the SOC is calculated directly from the voltage and not independent of it.

I don't know how the battery sensor in the car does it. The battery sensor measures both the voltage and current as well as the temperature. So, it probably uses all of the voltage, current, and temperature to determine the SOC, as the SOC-vs.-open-circuit-voltage relationship depends on the temperature, and knowing the current could be helpful for determining the SOC, too.

The long story short, look at the voltage values in your monitor with the car turned off, and then use the table I posted above to estimate the SOC. I don't think the SOC estimates of your monitor are correct.

 

I thought it must be a simple calculator, but it isn’t. Voltage can be 12 or 14 and soc can be the same. Soc is measured independently of voltage. While charging to 100%, the voltage is much higher, but the soc climbs steadily and never goes over 100%. When charging is over, voltage drops, soc stays the same. Many cheap products have state of charge indicators. Putting a load on a power tool, battery soc doesn’t dip.
Long story short, yes I do check the voltage with car off and parked. Since the monitor records for 5 previous days, can sit in an armchair and read it. The truck is a fairly straight line all night. The Prius has some tapering down, with sometimes a dip and back.
It may be only when the moon is full.