12v Battery/accessory Mode

[YarisHybrid2016]

Hi,

Apologies for all the questions! :D One of the things I noticed was that it states that if the vehicle is in ACCESSORY mode, if will switch off automatically after 20 minutes to try and prevent 12V Battery discharge.

For various reasons I can end up sitting in my vehicle for over an hour just listening to the radio. Is the auto-off function just being very protective, or due to the electric nature of the systems, will it flatten the Battery much quicker? If that is the case, no problem, but intriguing nonetheless.

A related question, is there any reason not to sit with the hybrid system running in PARK, or is it advised against for economy/battery reasons?

[cootuk]

Ii I'm sat for a while, I keep it in park, but turn off air con as that keeps firing up the ICE.

[Devon Aygo]

If you switch the car on but do not go into "ready" mode then you are using the small 12v Battery and can run the Battery down quickly hence the auto shutdown.

Once in ready mode the cars power comes from the Large hybrid Battery which when low on charge will start the engine to recharge only if you shift to neutral will you get a warning as the car cannot charge when in neutral.

[timberwolf]

It could significantly shorten the life of the 12V Battery - replacement within a year is possible if the charge is not being replaced. The hybrids have a weaker charging circuit than conventional cars - even if Toyota has improved them a little with later models.

[YarisHybrid2016]

Interesting.

Is it common for the 12V Battery to be replaced then? Would it be worth me getting a 12V Battery charger with conditioner/float charge function and put it on the Battery periodically to keep it in good condition? I'll use the vehicle maybe 2-3 times/week.

Would I be correct in thinking the 12V battery is simply an accessory battery then for when the hybrid system is shutdown, just to keep essential systems operating?

[timberwolf]

Yes, it powers the car alarm, remote key fob receiver, brake pump, etc, whilst the car is dormant. Starting the car, involves running computers and switching the relays to connect the high voltage Battery.

An intelligent charger may help. Possibily not so easy to use on some models due to the location of the 12v Battery or availabilty of jump start connections. Whether it is required depends on a lot of factors and unfortunately there isn't a simple, reliable set of rules to make that decision. I would guesd most people don't recharge their 12v Battery.

[theoilburner]

As it happens, we've just replaced the 12v Battery on our Prius. It's on Battery number 3 now. First Battery went after less than a year, battery number two lasted 5 years or so. We've never done any conditioning charge or whatever in the 2.5 years we've owned it. Although after leaving the car for 2 weeks whilst on holiday, it seems it would help it to give the battery a boost before using the car, as it never seemed to like that much. However, at £90 for a new battery (which I think is fair for 5 years use), I'm not overly concerned with it.

Just for the record, you'll know when your 12v is getting too low when the car starts doing strange things, like not going into Ready mode on the first press of the power button, or sections of the digital dash and HUD turning themselves off... Ours was down to 10v when I gave in and bought a new one. I'm amazed it even worked at all at that voltage really.

You can also check it's state by pressing and holding INFO-TEL whilst switching the lights on and off three times. On one of the diagnostic screens that pop up, you can see the 12V battery state. Do that when not in Ready mode to get a true reading.

[YarisHybrid2016]

As it happens, we've just replaced the 12v battery on our Prius. It's on battery number 3 now. First battery went after less than a year, battery number two lasted 5 years or so.

Hmm... interesting. Makes me think that it is the charge system of the car that is not looking after the Battery properly. Do you drive your car regularly (e.g. each day to work)? Given the Battery isn't being used to start the car (i.e. it is not being hit for 150A by a starter motor), either the Battery charger isn't working too well and/or something on the car is discharging it faster than other cars.

You can also check it's state by pressing and holding INFO-TEL whilst switching the lights on and off three times. On one of the diagnostic screens that pop up, you can see the 12V battery state. Do that when not in Ready mode to get a true reading.

Great tip, only I have a Yaris, not a Prius. Can something similar be done on the Yaris as well?

Interesting topic.

[MEP's Yaris GS]

Never had an issue with the charging system on my PiP, even after the Battery going completely dead in April due to leaving the interior light on for a week when left in an airport carpark.

It's just the nature of being such a tiny Battery it won't be capable of keeping the accessories running for extended periods of times like some other cars. Personally I never use accessory mode and just sit in READY if I want to use the radio etc to prevent using the 12v Battery on its own. Having it in READY will also help keep the battery topped up, 2 bird with 1 stone and that.

[Chris Dance]

I also use READY mode when listening to the radio and waiting for "her Indoors" etc. I seem to recall Grumpy Cabbie recommending this from the days when he was using his Prius as a taxi and he had a lot of waiting time. It is so easy to flatten the 12v Battery on a Toyota hybrid. Leaving the boot light on over night did it for me.

[theoilburner]

As it happens, we've just replaced the 12v battery on our Prius. It's on battery number 3 now. First battery went after less than a year, battery number two lasted 5 years or so.

Hmm... interesting. Makes me think that it is the charge system of the car that is not looking after the Battery properly. Do you drive your car regularly (e.g. each day to work)? Given the Battery isn't being used to start the car (i.e. it is not being hit for 150A by a starter motor), either the Battery charger isn't working too well and/or something on the car is discharging it faster than other cars.

We do use our Prius quite regularly, 3 days a week for long journeys to work, a couple of days of local short journeys and maybe a day at the weekend for general family use too. I'm not sure whether the charging system is naff or not, but it IS a very small battery and is probably a very cheap design given that it doesn't ever turn the engine over, like you say. Remember that the Prius also has keyless entry (pretty standard on Toyota now, I suppose), so it's always scanning around the doors and boot for a key nearby, that must take quite a bit of juice too. I've noticed how it puts the interior lights on if you walk past with the key too...

You can also check it's state by pressing and holding INFO-TEL whilst switching the lights on and off three times. On one of the diagnostic screens that pop up, you can see the 12V battery state. Do that when not in Ready mode to get a true reading.

Great tip, only I have a Yaris, not a Prius. Can something similar be done on the Yaris as well?

Interesting topic.

I think so (disclaimer - I haven't got a Yaris so can't try it!) - if you have one of the T&G type systems, then I think you'll have a Setup button (I do on my Avensis), you can press and hold that, switch the lights on and off three times and that will get you into your diagnostic screen, assuming you have a touch screen.

[YarisHybrid2016]

if you have one of the T&G type systems, then I think you'll have a Setup button (I do on my Avensis), you can press and hold that, switch the lights on and off three times and that will get you into your diagnostic screen, assuming you have a touch screen.

Yes it does. I'll try this and see if it does anything.

Remember that the Prius also has keyless entry (pretty standard on Toyota now, I suppose), so it's always scanning around the doors and boot for a key nearby, that must take quite a bit of juice too. I've noticed how it puts the interior lights on if you walk past with the key too...

That's a good point. I wonder if disabling the feature disables the sensors to save power? Could be useful if parking for a couple of weeks at an airport for example.

[MEP's Yaris GS]

I've noticed how it puts the interior lights on if you walk past with the key too...

You can get the dealer to deactivate this should you wish.