Understanding the two batteries

[purplefleece]

I need to understand what runs off the main car Battery and what runs off the 12v Battery  

I am newish to my Prius Hybrid 2018 Bus Edition model. 

A few months ago, the 12v Battery went flat because I’d been charging my phone in the car while the engine was switched off. I was in the middle of the countryside. The AA repair person changed the battery for me showing me the old battery was only 4volts or something and very bulged so at the end if its life. He put in a decent 12v battery. 

I’m now not sure what could risk draining the battery. Listening to the radio? Front doors being left open for a couple of hours because of the little lights in them? Charging my phone? Anything else? 

Basically, I don’t understand when the main electric battery that drives the car is in play and what the 12v battery does. Can anyone help with this?

[Yugguy1970]

Howdo.  I don't think you you need to worry too much.  Your old Battery was knackered and you'd been charging your phone off it with engine off.

As long as you don't do this with your new one you will be fine.  

It's never a good idea with any car, hybrid or plain engine, to stay in just ignition on/accessory mode for a long time, especially if then also using the electrics.

Put it in Ready.  Our hybrids are really good at not running the engine any longer than is necessary so it is OK to leave it in Ready.  Ready lets the big hybrid Battery charge the little 12v one, and lets the engine charge the hybrid Battery.

[Catlover]

To get a sufficient charge to your 12v Battery you need to be in Ready mode, as Guy said, for 40-60 minutes. For sure you engine will be running some of the but you may be surprised it will not be much, and it will be off more then it is on. Try not to use any car electric items whilst you doing this.  Depending on your situation, remember to keep you car secure whilst doing this charge, and definitely do not leave the car by itself on a public highway as it is a traffic offence (apart from being a stupid thing to do). Particularly in this cold weather and particularly if you do short journeys or not use the car regularly, do this charging at least once a week for an hour. If you go somewhere and your partner goes shopping and you staying with the car, put it in Ready mode to charge it up. 

[Harters]

Basically the 12v Battery is designed to power the computers to enable to 'start' the car and then run f the main hybrid traction Battery and not much else.  As everyone else has said, if you want to be running any equipment, make sure the car is in ready mode - foot on brake, then power button, instead of just pressing the power button.

Unless the Ready light is on, you are running on the 12v Battery.

If for any reason you didn't shut a door fully, the interior lights are designed to switch off after about ten minutes.

[Chris Dance]

 I left the boot light on overnight on my Prius gen 3 a few years ago. Overnight the 12v Battery was flat. If I am waiting in the car with radio on I keep it in ready mode. It does not take much to flatten the 12v Battery on a Prius. 

[john p williams]

30 minutes ago, Chris Dance said:

 I left the boot light on overnight on my Prius gen 3 a few years ago. Overnight the 12v battery was flat. If I am waiting in the car with radio on I keep it in ready mode. It does not take much to flatten the 12v battery on a Prius. 

Or in  a Honda CRV as a pal of mine recently found out.

[Roy124]

John, my neighbour bought a Kia.  Out of curiosity I had a look at their owner forum.  Battery woes feature there too. 

[john p williams]

14 minutes ago, Roy124 said:

John, my neighbour bought a Kia.  Out of curiosity I had a look at their owner forum.  Battery woes feature there too. 

I`ve had a Lexus for 11 years and I only have problems when I don`t use it for a month in cold conditions. The small jump start pack works a treat Roy.

[TonyHSD]

All has been very well explained already 👌 and I just like to summarise it for you and all others new to the hybrids: 

Hybrid Battery powers the electric motor and air conditioning only and charges the small 12v battery 

The 12v Battery powers up everything else like unlocks and starts the car, does diagnostics, pressurises the electric brake pump, , powers up infotainment, heated seats, electric windows and mirrors, lights, heating fan, and hybrid Battery cooling system, plus engine and inverter electric coolant pumps, and electric power steering,. pretty much everything including any additional devices like phones, tablets etc. 

Always keep the car in ready mode and select P on your gear selector while seating inside waiting for someone, do not leave the car in N neutral or with open doors when turned off or unlocked with key fob nearby for long period of time. 👍

[Duffryn]

I flattened the 12v Battery twice on my previous Gen 3 by inadvertently leaving the interior light on overnight. I flattened my current Gen 3 by not using it for a week (during lockdown), and prior to that doing only short journeys.

Now invested in a brilliant little Ctek charger which I plug into if the car isn't being used for a few days. Can well recommend the Ctek.

[Cyker]

Don't even think too hard about it, just follow this rule: If you're in the car, put it in Ready mode (i.e. hold down footbrake and press Start).

Getting ready to go on a trip, waiting for kids/wife/nephews to get ready? Put the car in Ready mode.

Waiting in the supermarket carpark for SWMBO to return the trolley? Put the car in Ready mode.

Getting in the car to play with the dash controls/dashcam/seat settings? Put the car in Ready mode.

Waiting outside school for kids in the car? Leave the car in Ready mode.

Waiting outside school for kids in the car in one of those zones where it says to turn your engine off to improve air quality? Leave the car in Ready mode.

Watching a film in a drive-in cinema? Leave the car in Ready mode.

Waiting to pick up a mate outside the train/tube station? Leave the car in Ready mode.

Eating a sneaky drivethrough MaccyD's? Leave the car in Ready mode.

Eating some horrible services food and want to isolate from the other plague zombies? Turn the car off, go in and buy your comestible of regret, return, put the car in Ready mode.

Sitting in a field looking at cows? Leave the car in Ready mode.

Sitting in a desert looking at capybaras? Turn the AC on, leave the car in Ready mode.

Hiding from a hoard of marauding zombies? Turn the lights off, leave the car in Ready mode.

You get the idea...  

[Roy124]

"Getting ready to go on a trip, waiting for kids/wife/nephews to get ready? Put the car in Ready mode." 

This is the only one with which I disagree.  The best way to warm up the engine is to drive the car.  As you are about to embatk on a trip it will get plenty of charging. 

Of course:

if the car is iced up put it in ready mode before you drive,

if the car is very hot put it in ready mode to get the air con working. 

 

[Catlover]

So, that thought process started 10 hours ago.

10 hours ago, Catlover said:. If you go somewhere and your partner goes shopping and you staying with the car, put it in Ready mode to charge it up. 

 

[purplefleece]

Really helpful explanations and advice.  All understandable. 
Thank you all very much. 

[AlyCat]

Quick question:  If a 2010 Prius has been sitting for over a year, the 12V Battery is dead, does that mean the hybrid is dead as well?  If so, is there some way to charge it if the 12V is replaced?  Any help is greatly appreciated.

[TonyHSD]

4 hours ago, AlyCat said:

Quick question:  If a 2010 Prius has been sitting for over a year, the 12V battery is dead, does that mean the hybrid is dead as well?  If so, is there some way to charge it if the 12V is replaced?  Any help is greatly appreciated.

Hi, after that long period of time I can’t tell for sure what would be the condition of the hybrid Battery, best thing to do is to fill up with fresh petrol 5ltr at least, check the oil , filter, spark plugs, air filter and replace if necessary, connect a new 12v Battery, you can also run a diagnostic before first start of the car to double check if any juice left in the hybrid Battery or simply start the car and leave it ON for at least 30 min, watch for engine temperature or any warning lights . If your hybrid battery is completely dead then you will need hybrid specialist who can diagnose and determine if the battery can be charged and save or you will need a new hybrid battery, they can also repair your existing one too. There are some traders on eBay or Google it and it will show you some results. 
Good luck and please share with us what happens 👍🔋

[Catlover]

I was once told by Toyota dealer that if the hybrid Battery is discharged, and we were talking about running out of petrol and trying to get home using hybrid Battery and empty it, then it would be difficult/impossible to get the hybrid Battery up again without the existence of a hybrid battery charger (not a standard nor smart charger) and there was only one in the area and it’s shared. So best ensure hybrid battery is fully charged before shut down for long time.

[AlyCat]

Thank you both so much!