12V dies every two years

If you find such a device please let me know. I am not aware of any such device to monitor the current or "amp" in mA precision but I would be interested in trying one if exists. I am using a BlueTooth battery monitor (QUICKLINKS Auto Battery Monitor MB2 www.amazon.com/QUICKLYNKS-Battery-Monitor-Bluetooth-Device/dp/B01MT4583U) installed on my PP battery. It monitors the electric potential difference or "volt" in 0.01v accuracy. Unlike you, my PP sits on the driveway undriven for days in between. My aim is to keep the 12v battery voltage above 12.4v. If it drops below 12.3v, it warns me that I need to charge the battery. If I don't plan to drive for a while then I plug a smart battery charger/maintainer.

If you have your hypothetical device on the car all the time, it is very important to be able to distinguish when the car was resting without any electrical system including charging and battery thermal management. Otherwise, you will never be able to tell if the "phantom" draw is excessive or not.

Here is the graph of the last 15 days of battery monitor data. As you can see the 12v battery voltage dropped to the lowest point of 12.36v after sitting 3 full days undriven.

 

The 12 volt battery is maintained by the hybrid battery through the inverter’s converter to converter (hi voltage dc to low voltage dc). Assuming the computer is up to date (as you verified) then even with an above normal parasitic draw (with in reason) the 12 volt battery should be being maintained with your driving habits and the battery should last a lot longer. PERIOD
Since it is not then that indicates a problem with the charging system. PERIOD The dealership should be looking hard at the inverter assembly. As you suspected, something is wrong and you shouldn’t have to be the one trying to figure it out since it is pretty evident that it has been there since day one or so after the original owner took possession of it.

 

This is all part of the hybrid system and should still be covered under warranty (probably even at least one of those battery replacements).

 

I don't think your voltages are accurate. 100% SOC should be 12.7 V, but yours is showing about 12.4 V. Or perhaps it's because you are not measuring the open-circuit voltage. Therefore, it looks like your SOC hardly dropped in three days. This summer I left the car off for about 25 days, and I had no issue with the 12-V battery whatsoever.



https://www.researchgate.net/figure/1-SOC-vs-no-load-terminal-voltages-of-a-typical-12-V-lead-acid-battery_fig5_337338929

 

I had mine die a few times during quarantine since I wasnt driving that much. Also found out my Comma.Ai kept drawing power with the car off. I disconnected it about a year ago and the battery has been fine.... until today. I think, based on earlier posts, that my battery has kicked the bucket. Luckily it was a benign failure since it happened in my driveway. I've got a battery tender on it now, I'll likely try the "battery repair" feature which pulses 15V on and off every couple seconds for 4hrs. But I feel thats more of a bandaid than a solution.

Sounds like OP has some kind of constant power power draw. Mine was an OBDII attachment (part of the comma.ai system). I think I solved the problem too late though.

 

So, perhaps the Prius Prime keeps the 12-V battery SOC in the green zone below 80% to maximize its life. Apparently the ideal 12-V battery SOC is between 50–80%. That's why using a trickle charger, as some posters do here, could actually reduce the battery life by overcharging the battery above 80% SOC.

 

The 12.7V is an average. It is higher for gel and AGM, while a little lower for flooded batteries.
https://footprinthero.com/lead-acid-battery-voltage-charts

The ideal state of charge for lead acid is 100% as dipping into low charge states shortens the battery life. Best would be to have a float charge from a tender going into the battery.

All batteries self discharge over time. Even when not hooked up to anything. For long term storage, a lead- acid battery should have its voltage checked, and charged back up when the SOC reaches 70%. Sooner would probably be better.

Battery storage tips and state of charge dos and don’ts | Simarine
How To Safely Store Lead-Acid Batteries - News about Energy Storage, Batteries, Climate Change and the Environment
BU-702: How to Store Batteries - Battery University
BU-403: Charging Lead Acid - Battery University

 

Here is more detailed data and a summary of my previous PP (2020) when the car was less than 2 mo old. But the car was kept parked more often than driven. On average it was driven only once a week. It is clear that PP has some "normal" drain when parked. The 12v battery in PP almost always drops down SOC (resting volt) daily.

If anyone cares to read the discussion, here is the link to the thread that dives much deeper into this subject.
12v Battery Is Discharging, Re-Charge Now ! | Page 11 | PriusChat



Some observations with 2020 PRIME LE, driven once a week (plus additional short drives in 3rd week).

• using an external charger brings the 12v battery SoC higher (~13v) than using an on-board internal charging system (12.7v-12.8v)
  
• max SoC by on-board internal charging system decreases slightly each week (12.81v, 12.79v, 12.76v)
  
• first 24-48 hours 12v battery drains most at ~0.1v/day and less drain/day subsequent days
  
• ~1.5hr once a week drive is sufficient to keep the 12v battery SoC to stabilize around 12.4v after 5 days
  
• short 10 miles drive is insufficient to bring the 12v battery SoC 100% (12.7v)
  
• ~3.5hr L1 charging had almost no effect in replenishing 12v battery SoC (from 12.38v to 12.42v)
  
• turning SKS OFF from the fob had no effect on the 12v battery drain

 

Every battery is manufactured to specific standards by the manufacturer and “Full SOC” is actually specified by the manufacturer (not by some generic chart). Additionally, every charging system is designed with a specific Full SOC in consideration. Regardless of what beliefs or opinions each of us may hold, the system design is what determines what a full SOC actually is. Full charge for a lead acid battery can vary (depending on manufacturer specs). Check out Weber University’s YouTube channel and you’ll hear the advice given to insure your replacement battery meets the specs of the manufacturer, not “what ever fits in the space” or you will likely have problems. Check the specs for Toyota Priuses. Just maybe some will be surprised what they find (if they are actually interested in facts instead of beliefs or “personal experience”).

 

AMAZING!! Two devices that require power to operate used no power to communicate (“turning SKS OFF from the fob had no effect on the 12v battery drain”). These Priuses are even more advanced than previously thought! Perpetual motion here we come! Yahoo!

 

As I said earlier, most of these chargers are overcharging the 12-V battery, which harm the battery and can cause quick failure. The battery should never be charged beyond 12.8 V. If you are going to use a charger, find an advanced one that you can set the voltage limit etc.

 

Not exactly; sure what your definition of an "advanced" charger is, but before owning a PP, for over 30 years, I have used probably what you would consider a "non-advanced" or "dumb" manual charger shown below. I have used it on half a dozen car batteries in the past without a problem. I have never had any car battery fail in less than 6 years.



But after having read many PP and Gen4 owners reporting the early demise of the 12v battery, I decided to invest in what I would consider an "advanced" charger, Victron blue-smart-ip65-charger with an advanced electronic "smart" brain.

But, either a "dumb" charger or a "smart" charger will charge the battery at the highest set current during the first bulk phase of the charge which usually results in higher than 12.8v. I have not had my PP's OEM12v battery by GSYUASA fail so far in the last 5+ years, although the longest I owned was for ~3 years with 2017 PP.


With my current 2021 PP, I drive it, at last, a few times a week, so I am not too worried about the 12v battery. But if it sits longer than a week and the resting voltage drop below 12.3v, then I replenish it by charging it with an external charger. However, I don't have any comparison to make in terms of the longevity of the 12v battery with or without occasional external charging when it is not driven frequently.

For the inevitable day in the future, I carry a battery starter pack in each car I own. In my PP, I actually have both a lithium battery pack jump starter and a super-capacity jump starter, but so far, I have not had a chance to use either of them.

 

Well, I did not say SKS uses no power, I just said “turning SKS OFF from the fob had no effect on the 12v battery drain”. The drain was not stopped and the rate of the drop was not appreciably slowed by turning off the SKS, thus the conclusion is that the power used by SKS is not the only factor causing the 12 v battery drain. Or at least it is not the major power drain source. It could well be a small part of the whole normal drain on the 12v battery, but by itself, there is not a huge draw.

 

The Battery University site lists a charge voltage range for a 6 cell of 13.8 to 14.7 volts. The Scangauge report for the variable alternator of the HHR was mostly in that range. Sometimes it would go over 15V, but it can be charging the battery and running accessories at the same time. Engine off, the display dropped to 12.x.

The potential over drain from the SKS happens in cases where the fob is stored within range of the car. Then the system on the car stays awake, waiting for someone to get in and drive off. You not seeing a difference means the fob signal wasn't reaching the car because of distance or shielding. Putting the fob to sleep might have extended its battery life.

 

If you care to know the voltage setting for the Victron "smart" charger, here is the excerpt from the manual. Yes, I can customize the charge voltage to lower than the Normal setting, but it is not recommended as per the manufacturer's instruction. So, I have never changed it. I always use it with Normal with low current (2A).

Well, the above result was tested with the fob turned off from the fob buttons which does not deactivate the SKS system in the car, but only disables the fob from receiving the radio signal. With this mode, the only thing turned off is the fob, and thus it saves the "coin" battery in the fob but does not affect the 12v battery draw in the car much at least not under my use condition.



However, later on, I repeated a similar experiment using Carista to specifically "stop" the car from monitoring the fob signal, essentially "disabling" the SKS part of the car. The result was very similar to turning off the fob. By itself, it did not change the rate of drain from the 12v battery appreciably.


Default value is 5 days:

This battery-saving feature is also stated in the manual. Essentially, by default, after 5 days, the car will shut down SKS on its own. With Carista (or with Techstream?), I can change that wait to 0 days. But it did not prevent the "normal" drain rate of the 12v battery on my PP, at least not to the noticeable level.

 

Does the system have a battery type selection? Part of the voltage range given by Battery University is that it is better to charge AGM/gel batteries at a different voltage than flooded ones. My Viking charger from Harbor Freight has such a selection.

My gen2 Prius had a physical button under the driver's seat to turn off the SKS system when parking the car for an extended period, like over a week in an airport parking lot, to avoid draining the 12V. The SKS system got 'smarter' over time, puts itself to sleep when a fob is outside of range, and the components for the occasional pinging are now more efficient. Unless the fob is stored close enough that both sense the other, the system on the car is mostly shut off. If that's the case before making changes to the fob or car settings, nothing much will change afterwards.

 

You don't need to charge the battery unless you are going to leave the car undriven for more than a couple of weeks or so. However, your various devices connected might be draining the battery. Prius Prime has a much more smarter charging system with a battery sensor that optimizes charging. Overcharging (charging to an open-circuit voltage above 12.8 V) is bad for the battery.

2. Overcharging

While you certainly don’t want to keep your battery in an undercharged state, overcharging is just as bad. Continuous charging can:

• cause corrosion of the positive battery plates
• cause increased water consumption
• even allow for excessive temperatures causing damage inside the battery.

This continuous heating from overcharging can destroy a battery in just a few short hours.

Most common lead–acid battery mistakes | Northeast Battery blog