12 Volt Battery drain Gen5

just install a Noco genius!

 

i think there is more drain, a lot of people seem to be in your situation

 

I would be sceoptical. Any 12 volt battery drained to 4 volt will not last much longer, if at all.

What's your parking situation? Do you have secure, off-street parking with 120 volt AC outlets available? If so,l look it smart chargers, around 5 amp rating, either on-board or exterior to the car, depending on the situation: if you're parking outside an onboard charger is more secure, just a power cord protruding from grill (like a block heater cord) is the usual setup. If you're in a secure garage you could also use an exterior-style charger.

My setup:

 

The 12 volt battery discharge problem is common for the generation 5 prius.
The problem has several causes including:
The remote control too close to the vehicle for example when washing and/or waxing the vehicle or even in the garage during maintenance.
Those who do not close the Toyota application after use.
The fact that if the temperature is above zero Celsius, the DC-DC converter charges the 12 volt battery only 5 minutes after the vehicle leaves, after which it only maintains it.
When you recharge the high voltage battery, it's the same, you only recharge the 12 volt battery for 5 minutes.
In short, we discharge it more than we recharge it.
On this document:
Toyota/Lexus 12v Battery Failures - Analysis of Charging Issues - Deep Dive Analysis & Workaround by /u/andy_why - Google Docs
It is recommended to disconnect the connector near the negative terminal of the battery so that the DC-DC converter always charges at 14.4 volts (not just 5 minutes).
To find out the state of health of your 12 volt battery, test your SOH, if it is less than 75%, it should be replaced.
The SOH gives the remaining capacity of your battery, for a 45 AH battery at 75% SOH, this means that there is only 34 AH of capacity remaining.
It is easy to find and buy a tester that measures SOH, garages also have this tester.
Using a smart charger is a good idea, but avoid NOCO where you stay, because it barely charges the battery to 60% when the temperature is below zero Celsius (poorly temperature compensated).
The best smart chargers for very low temperatures are the BATTERY TENDER.

 

Didn't know that about the low temp performance of the NOCO. You live in a cold weather testing laboratory, so you should know!

 

You can charge the 12 volt by putting the car into “Ready” with a charged up Traction battery. Shutting off the heater will prevent the engine from running.

I believe that you can lock the car with the manual key.

Leave it for 4 to 6 hours.

Unplugging the battery monitor at the negative terminal, as suggested by Danny Dan, will also help, but in cold weather the charge voltage should remain above 14 volts without doing so.

 

This all sounds very familiar. I have experienced many dead batteries, which happens at unpredictable times. I alerted the dealer to the problem, but they informed me that the factory battery was testing up to spec. Another dealer actually replaced the battery, to no improvement at all.

I have my own theory; I believe the live updates are draining the battery at variable and unpredictable rates. Sometimes the 12V battery will hold a charge for a week, but other times, it drains in just a few hours.

I believe this to be a design flaw, but since no update or recall is available, I have resolved myself to using a battery maintainer and a booster pack.

This all could have been avoided if the system were designed to maintain the 12V battery off the hybrid battery.. We can only hope that Toyota will someday see the light and fix this problem.

 

I've had poor luck with "smart chargers."
They tend to shut down if the battery isn't in top condition.

 

Next, when I went to the dealership for service 2 (oil change and inspection), I plugged in my 3 amp smart charger to recharge my 12 volt battery when I returned.
To my surprise it took 5 hours to recharge it, that means they drained 15 AH from my 45 AH battery.
They therefore discharged the 12 volt battery by 33%.
If the temperature is above zero Celsius and the DC-DC converter only works for 5 minutes, it will take a long start to recharge it and in the meantime it will have time to sulfate.
This is why some people disconnect the connector near the negative terminal of the 12 volt battery to force the recharging of the 12 volt battery with the DC-DC converter.
Don't forget that if the temperature is below zero Celsius, the DC-DC converter always charges at 14.4 volts.

Note that the last update of the Toyota application, Toyota corrected the problem that the application remained functional in the background after closing their application.
We had to close the duplicate application, close the application and close the background application.
If we did not close the application in the background, the application remained in communication with the DCM and drained the 12 volt battery.
Now, when we close the application, we close both.

In summary, to maximize the life of your 12 volt battery:
Always deactivate your remote control when washing your car, waxing it, sweeping it inside, shoveling snow, shoveling around the vehicle and/or being near your vehicle.
Always recharge your 12 volt battery after a visit to the garage or your dealership for oil change, tire change, service (inspection), repair, etc.
Always close your Toyota application correctly after use.
And optional, if you don't mind losing a little battery life, unplug the connector near the negative terminal of the 12-volt battery.
Finally, I recommend purchasing a BATTERY TENDER smart charger (better than NOCO) especially if you live in Canada.

 

My car (not a Prime) is still new. I'm still in toy-buying mode. This toy is nice: