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Phlipper

Newbie & Paranoid Might Run 12V Battery Flat!

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I've been doing a lot of research and will be picking up my Gen 3 next week, but whilst doing my research I've come across a lot of people saying they've inadvertently run their 12v Battery flat leading to all sorts of difficulties.

Can anyone suggest some sort of charger just in case I do manage to run it flat and do you have any advice for a newbie?

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I would say turn off the boot light as that is the main one that can stay lit without you knowing and drain the Battery.

Other than that, you shouldn't need to trickle charge, but be aware of how to start the car from another Battery should the need arise.

Be prepared to change the 12V Battery when symptoms appear...not sure if you can access the GenIII diagnostics like you can a GenII..if so you can keep an eye on the 12V through there every now and again.

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In the two Prius that we have had, and our new Yaris HSD, we've never run the Battery down. Not even close, and our last GenIII T-Spirit had all the toys on it, including adaptive cruise, heated seats etc....

How do you 'expect' to run the 12v down? Remember, it isn't used in anger for anything serious, just to keep the on-board electronics alive, and to 'start up' the HSD inverter etc when you power the car up. Once the car is 'booted up', the engine is started from the MG via the HV Battery - the 12v has nothing to do with that. And the Battery doesn't have to suffer the massive cranking current discharge each time the car is started, so is kinder to the Battery overall.

Unless you intend to run some serious lights and a kick-***** sound system, parked up in the local Asda car park until 4am with the HSD off, or are very careless with the interior/boot lights, I really can't see it being an issue.

Now my Range Rover is a totally different story ....... that DOES need to be tended and trickle charged.

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Well, I don't think I'll be turning up at the local boy-racers hang out in my Prius any time soon ;) I'll turn off the boot light and just make sure to leave nothing on that shouldn't be. (I've even heard the keyless entry system can run the Battery flat as it actively 'looks' for 'key's if any pass by. Things like that, I guess, had me concerned.

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I would say turn off the boot light as that is the main one that can stay lit without you knowing and drain the battery.

Other than that, you shouldn't need to trickle charge, but be aware of how to start the car from another battery should the need arise.

Be prepared to change the 12V battery when symptoms appear...not sure if you can access the GenIII diagnostics like you can a GenII..if so you can keep an eye on the 12V through there every now and again.

What are the symptoms of a dying 12v Battery?

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What are the symptoms of a dying 12v Battery?

The first noticeable symptom was my 12 volt Battery going flat at the airport parking over the space of a two week stay. The cure was very close at hand in that I had just purchased one of those combined emergency lamps, air compressor and booster Battery packs and had left it in the boot as a precautionary measure. The Battery has not gone flat during the three months since that incident but I know it is on its way out and I am ready for it. In the mean time ,I am researching a replacement Battery at my leisure. The booster Battery is being kept charged up from my on board 12 volt socket, by the way.

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If you are concerned about breakdowns join Toyota Club which includes full AA membership breakdown service.

If your 12v Battery goes flat the AA will sort it out for you. I did not shut the rear hatch properly on my previouus Gen 2 Prius and the interior light discharged the 12v Battery overnight. I called Toyota Club and at that time they used the RAC. The RAC chap came within an hour and using the procedure outlined in the owners manual very soon had me going.

I now have a 2011 Gen 3 and I keep the boot light and interior light off when parking up. At every service I ask for a check on the condition of the 12v Battery.

Tips. Keep boot light and interior lights off when parking up. Always ensure rear hatch is fully closed. If the 12v Battery fails only use the procedure outlined in the owners manual to get started.

I do not know what symptoms you would get for a failing 12v Battery. Mr T says 12v Battery life is about 4 years, There is a way to check the 12v Battery condition yourself. There is a thread on this somewhere on this site but at the moment i cannot find it,

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The cure was very close at hand in that I had just purchased one of those combined emergency lamps, air compressor and booster battery packs and had left it in the boot as a precautionary measure.

I have one of those and although I don't normally keep it in the car, I plan to put it in the boot if I have to leave the car for a long time. An alternative is to connect a solar charger if the car is in the daylight.

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A Battery is dying from the moment it is made. The useful life that you can get from a 12V Battery is going to vary depending on various factors, but I think the only one an owner can influence is how the Battery is used/abused. Lead acid batteries do not like remaining under-charged for long periods, it shortens their lifespan. The lifespan can be anywhere from as little as a year, 4 years seems to be typical, and there are owners that get more than 4 years, the latter no doubt wonder what all the fuss is about when their Battery has lasted so long.

Case A:

If a 12V Battery has gone flat by accident, for example because an interior light was left on overnight or the hatch not shut properly, that will result in a shorter lifespan.

Being forgetful or careless is something that can most likely be solved by a change of behaviour, how quickly someone learns depends how inconvenient they find it not being able to unlock or start-up their car. I think all the useful tips have been given already?

If you are buying a pre-owned car, you've no idea how the previous owner may have mistreated the Battery, or if the dealer may have left the car unused for too long.

Case B: (I'm paranoid but I have reason to be :lol: )

A 12V Battery that is not fully charged and then left for long periods is going to have a shorter lifespan then those that are regularly charged up.

Infrequent use/very low mileage, such as using the car only at weekends or once a week, this is where you may want to consider a good quality 12V Battery charger - as it can extend the lifespan at the inconvenience of having to connect a Battery charger. I can recommend a good charger if you think you need one, and there are some small risks to be aware of.

Symptoms of a slowly dying Battery, you usually don't get too much warning in my experience. The door locks may be sluggish to operate. When you try to start-up you may get an exclamation triangle, all the dash lights may light or the dash lights may act weird. You may hear that the relays are slow when you start-up. On the few occasions where my Battery voltage got low, I was lucky and it was possible to start-up the car after 3 or 4 attempts.

I've tried monitoring the 12V Battery health by measuring the Battery voltage, but I have not been successful in being able to predict when the 12V Battery was going to need replacing.

Note: The Battery testers that garages use are not reliable and often report a good Battery health when it will fail again e.g. overnight.

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I forget about...

Case C:

As the 12V Battery gets older how long you can leave the car undriven on an infrequent basis (e.g. a holiday) will get less.

For example, for a new 12V Battery, fully charged, it is easily possible to leave the car for 4 weeks and it will still be able to start-up the car.

A four year old Battery, you may get anywhere from a few days, a week, two weeks... it can vary so much.

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Thank you all for your replies.

As mine is an 09 I need to prepare I think; so I'll be getting one of those Battery charger/air compressor thingies.

The car comes with AA / Toyota Club, so in an emergency I'll have some help on hand.

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Well, I don't think I'll be turning up at the local boy-racers hang out in my Prius any time soon ;)

Why not? You can surprise quite a few boy racers from a standing start.

Your mpg will take a hit but it is fun.

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Thank you all for your replies.

As mine is an 09 I need to prepare I think; so I'll be getting one of those battery charger/air compressor thingies.

The car comes with AA / Toyota Club, so in an emergency I'll have some help on hand.

The AA have their own Jump Starters so you could save some money and not buy a Jump Starter/Air Compressor thingie.

BTW the little Jump Starters that only come with a cigarette lighter plug style cable are no good for a Prius because the Aux power socket inside the car is disabled when the car is off.

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BTW the little Jump Starters that only come with a cigarette lighter plug style cable are no good for a Prius because the Aux power socket inside the car is disabled when the car is off.

My booster has high capacity leads to connect to the cars power system when required and a cigar lighter plug in order to keep it charged up while my car is running. I have never seen a booster starter which provide a boost through the cigar lighter socket itself. Are they quite common?You quite rightly point out that trying to boost a Prius through the cigar lighter socket wont work, besides which it would be the wrong point of connection.

Having waited for hours in the cold for a breakdown service to turn up, I prefer to have my own contingency plans on hand for such instances which are so easily and quickly solved as a flat Prius 12volt battery.

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No, not as common as the conventional kind of Jumper Starters (or Jump Starter/Air Compressor), but they are available and apparently about as much use as a chocolate tea-pot! I'm not sure what made me think of them, the thought just popped into my head...

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How about this for Battery life, not a Prius but an amazing example.

SWMBO had a ford 2002 Focus Diesel, used mainly for very short journeys 0.5 miles to 3 miles only. She had problems with slow cranking 4 years ago so, due to the nature of use and the age of the Battery (7 years old then), I assumed the Battery would be about ready for a change, so fitted new Battery. Still had the slow cranking, turned out to be started motor, which was then replaced. Old Battery was kept in my garage, not quite fully charged but not far off.

She gave the car to the daughter 3 years ago, when she bought her Prius Gen 2. The daughter had to sworn the car 18 months ago (for reasons we'll not go into). She comes to put the car back on the road last week after standing for 18 months and the 4 year old Battery is now not holding a charge. I charged the old, now 11 year old, Battery up overnight and they fit it to the car, lo and behold this 11 year old original Ford Battery that had been left standing in my garage for 4 years unattended, except for the one overnight charge before fitting, is working perfectly.

Does this mean these big (650 CCA) old Diesel batteries are more reliable or is it just a fluke ?

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Diesel is just *better* :D

But yeah, diesel batteries are built to take a massive pounding (the cranking force for a diesel engine is much higher than for petrol and would quickly kill a Battery only specced for petrol starter motors) so it seems right they'd be hardier.

I know there are quite a few of us diesel Yaris Mk1 owners who've still got the original batteries and still running fine!

What I'm surprised at is that it fits in the Prius! I thought the Prius Battery-bay was quite small whereas diesel batteries are usually pretty big - The one in my brother's Corolla 2.0D4D looks like it came out of a van! :lol:

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Diesel is just *better* :D

But yeah, diesel batteries are built to take a massive pounding (the cranking force for a diesel engine is much higher than for petrol and would quickly kill a battery only specced for petrol starter motors) so it seems right they'd be hardier.

I know there are quite a few of us diesel Yaris Mk1 owners who've still got the original batteries and still running fine!

What I'm surprised at is that it fits in the Prius! I thought the Prius battery-bay was quite small whereas diesel batteries are usually pretty big - The one in my brother's Corolla 2.0D4D looks like it came out of a van! :lol:

I didn't fit it to the Prius, it was put back in the Focus.

But what I was saying was is it the fact that these batteries are heavy duty that make them last longer ?

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No, I don't believe that the heavy duty Battery is any different in terms of obeying the laws of the universe i.e. from what I've read all lead acid batteries have the same types of properties and suffer from the same problems. I guess it is just relative.

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A little OT. When I was young, I remember a visit to the Science Museum, and they had an exhibit with a Battery and bell, the claim was it had been ringing for over 100 years. I don't remember the details but it maybe similar to this experiment, apparently rang for 170 years.

http://www.atlasobscura.com/places/oxford-electric-bell

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You can get 12V batteries for different applications. Car batteries are designed to crank starter motors. Leisure batteries are designed to provide current over a long period. Toyota hybrids don't need a typical car Battery so are fitted with a leisure type Battery (smaller and cheaper).

Check out Battery duty cycles..

http://www.mpoweruk.com/how.htm

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You can get 12V batteries for different applications. Car batteries are designed to crank starter motors. Leisure batteries are designed to provide current over a long period. Toyota hybrids don't need a typical car battery so are fitted with a leisure type battery (smaller and cheaper).

Check out battery duty cycles..

http://www.mpoweruk.com/how.htm

Thanks. I think the Lead Acid specific section on the same site, http://www.mpoweruk.com/leadacid.htm, is more useful because these batteries have specific advantages and disadvantages. For example, even if you have a Lead Acid Battery designed for deep discharge applications, e.g. a golf cart, my understanding is that it still needs to be recharged immediately after use and should not be left in the discharged state.

Why did the Battery for the diesel car survive, I think part of the answer is that they have to add a lot of extra capacity to cope with the demands of below freezing temperature cranking.

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