Charging A Prius12 V Battery Basic Help Needed

[stressed son in law]

I need some help.

My father in law has gone on holiday and given my wife the job of running his prius periodically to keep the Battery charged. In spite of these efforts (probably because of the condition of the Battery - its a car which isn't used much) the Battery is now totally flat. Nothing lights up at all.

I have never used, started, driven, and hardly ever been in a Prius!

Faher in law thinks I am a great disappointment to him anyway so I have read up how to charge the 12 V battery, followed the instructions (I think), and what happens is that when I switch the charger on all the dashboard lights flash on and off when on on high charge, and on low charge the engine management light flashes on and off. I have quickly disconnected the charger and am panicking and wish I hadn't interfered with it.. Have I messed it up? Am I doing something basic wrong. Is there a peculiarity about the prius?

Oh and I don't have the manual, don't know the model (only that it is 4+ years old) and am running out of time. I can't jump start it because it is in a garage.

I would be very grateful for some practical help otherwise I might have to just own up to Father in law or put everything back together and not tell him I've tried to charge it!

Thanks

[Chris Dance]

Being that the car is four years old and it is the original Battery the 12v Battery has most likely failed completely.

As you do not know the car and don't have a manual I would suggest you do not mess with the cars electronics. If you or your father in law are in the AA or RAC and have the home breakdown service call them . Better still if your father in law is a member of Toyota Club he gets AA service as part of the Toyota Club membership. He should have the club membership card in the car.

Starting the car is done by the starting point on the engine compartment NOT directly to the Battery. DO NOT attempt to jump start the Prius.

The only other suggestion I can give you is contact the local Toyota dealer for help.

I do hope you get it sorted. Just tell your father in law the 12v battery failed he should understand if it is the original battery.

[stressed son in law]

Thanks. What you suggest is my fall-back position which unless I get some other advice I will have to do.

By the way I connected to the +ve by the fuses and a negative bolt in the engine compartment.

Perhaps I'm old fashioned - or just inquisitive but as a relatively intelligent, practical person who likes problem solving I always seek to understand the things I own, work with, and depend upon. I may conclude that I need an expert (like a gas fitter, electrition, surgeon etc. ) to do the work but increasingly the answer to everything is phone an expert (and pay them) which is a bit of a shame. Of course it leads to my Honda garage charging me £102 an hour to change the oil and air filter on my vehicle which is ok if but.......

Thanks

[twohats]

Have you left the Battery on charge for while before trying to start? You know you need your foot on the brake to get the Prius into 'ready'?

Though I agree with Chris, sounds like the Battery has expired and has very low capacity, you might get the car started if it is charged for a while.

[steverally]

By the way I connected to the +ve by the fuses and a negative bolt in the engine compartment.

If you connect a slave Battery as above, inside the car try the normal start up procedure (press foot brake, press start button) DON'T put car into Drive mode. C

The display should activate and the cars IC engine should start, you could then remove your slave Battery, and cars engine and HV traction Battery should put some power back into the cars 12V battery. As Chris says though if battery is shot it will not hold the charge for long.

[timberwolf]

I would NOT recommend using a spare 12V Battery to provide a jumpstart in that way, there is no current limiting device built into the spare Battery (it is just battery).

[steverally]

Timberwolf, confused by your comment, as even in my lexus that is the recommended way of jump starting vehicle according to the manual. Ok they talk of Battery being in another vehicle.

My comment was for connecting the slave Battery to the jumpstart pillar in the fuse box in the engine compartment, not directly to the vehicle 12V Battery in the boot. Would not the battery protection be in the vehicle?

I must add though I've never had to follow this procedure with 3 years prius ownership and also with my current lexus.. so just following manual instructions.. or how I interperate what they mean.

[ian rooke]

Hi what current limiting device is fitted to the Toyota 12v Battery any such device would I would have thought would be inbuilt in the cars electrical system.

[timberwolf]

Worst case scenario, the original dead 12V Battery in the car had a short-circuit. You connect a spare 12V Battery to the jumpstart point, the 100A fuse block hopefully blows as you've just short-circuited a fully charged 12V Battery. Jumpstart your car from another carries the same risk. Jumpstart from another car carries added risk, as the electrical environment in the other car may not be a clean supply, so there is a risk that unwanted voltage spikes could damage an ECU.

If you are stranded and there is a life threatened, sure I'd gamble on the small risk. If it is just a matter of being a little inconvenienced I'd call a breakdown service, or replace the original 12V battery myself.

[steverally]

Thanks Timberwolf for explanation... not really planning to let Battery ever get to that state... don't want to explore your senario.

[ian rooke]

Thanks for that Timberwolf good explanation food for thought.

[timberwolf]

Edit:

Sorry, I am have a bad day, I have thoroughly confused myself. The DC/DC 100A fuse appears to be on the 12V side of the converter according to this http://priuschat.com...amp-fuse.82978/

[stressed son in law]

Hi again.

Thanks for taking my thread on. I have decided to leave the job well alone and get FIL to call the breakdown people..

Why did the instruments flash on and off like that though? Anyone know?

Isn't it interesting how things which 30 years ago was a part of the routine knowledge most car owners would have (Battery charging, jump starting, oil change, bleeding brakes etc) has now become something which even knowledgeable and enthusiastic 'owners club' members treat with trepidation.

I am keen to see what the breakdown man does, and what equipment and knowledge he will have. In my experience they are usually able to sort these things very quickly and effectively. Any bets on what he will do?

[timberwolf]

The car dash has been known to do weird things when the Battery voltage is low although that is usually when trying to Power the car on to Ready. I've never let my 12V Battery run completely flat, so I'm not sure what happens when you try to revive one from that state.

If your Battery charger is like mine it will a have limit on the maximum Amps it can supply and that is probably insufficient to power the car on. Toyota recommend that the 12V battery is only charged at 4 Amps maximum. To charge up a flat 12V battery (assuming it will take a charge), it could easily take 24 hours or more.

[kithmo]

If your battery charger is like mine it will a have limit on the maximum Amps it can supply and that is probably insufficient to power the car on. Toyota recommend that the 12V battery is only charged at 4 Amps maximum. To charge up a flat 12V battery (assuming it will take a charge), it could easily take 24 hours or more.

From my experience with SWMBO's Gen2 when it had a flat 12v, it took a momentary 30A surge from the Battery to flip the relays to the HV Battery so, assuming the Gen3 is similar, there's no way a normal Battery charger would be able to jump start the car.

To the OP, don't panic, connecting as you did, you can either put the battery charger on and leave it to charge for an hour or two or attach a battery booster pack, or jump from another battery, which will start it straight away. Just make sure you get the leads the right way round, red +ve to the fusebox connector and black -ve to earth, or you'll fry the electrics. Personally, if the Father in law is not due back yet, I'd probably put the charger on and leave it overnight.

[wass]

Having recently encountered our Gen 2 Prius with a flat 12 volt Battery, I can advise the following:

I used a booster Battery connected to the fusebox terminal and an earth stud as you described. I left that booster Battery in place, and the first thing which occured was the burgular alarm sounded and needed to be reset by pressing the unlock button on the keyfob. I then turned on the car in the normal way by pressing the brake pedal and start button symultaneously. Next, I waited for the engine to decide that it wanted to start up in order to put some heat into itself. Once the engine had started up, I disconnected the booster battery, closed the fusebox, closed the bonnet and drove away. Upon arriving at home, I reset the clock and retuned the radio stations. Despite your best intentions, your father in law will most likely comment that he can no longer find "MoanFM" since you have retuned his radio for no good reason. Sometimes you just cant win. :)