Recharging after Dead 12v Battery

Today, I came back to my Prius after leaving it for only a few hours. And to my surprise the battery had died. I called someone and jumped the car back to life. Then took the car for a little drive back to my house and turned it off, seeing if the battery would still hold some charge. But i came back out to it 10 minutes later and the battery was dead again. I hooked the battery up to a charger and let it run for awhile. Any suggestions on what i should do?

Your battery may have gone bad. You might have to replace it.

Let the battery continue to charge until the charger believes that the battery is fully charged. Then try using the battery and see if it dies again or not. If it does die again then it needs to be replaced.

Although it's a bit of a PITA due to the vent tube, cooling duct, and other "stuff" it's best to actually remove the battery and charge it with a dedicated charger.

Toyota used to recommend a fancy-schmancy automatic battery charger made by Associated, set at the 10 amp position. They now recommend a *very* fancy-schmancy automatic charger/tester made by Midtronics.

No, I don't expect anybody to rush out and drop +$800 on a battery charger. Any good automatic battery charger will work

With the battery fully charged, if you have a second vehicle take a drive to the nearest Pep Boys or Autozone - or similar place, NAPA, etc - and ask they perform a "load test" on the battery.

If it fails, the battery is kaput and you need a new one. This is pretty much a Toyota-only part, although with modification a Mazda Miata battery will fit. Optima makes a battery now too. For more details check out darrel's site or hobbit's site, many illustrated steps

If the battery passes the load test, take it home and charge it up again - it will be a bit discharged after going through the load test. You will then have to look for a drain somewhere

I agree with Jayman, you should be able to charge it. I have heard that it can take the higher "10 amp" position for several hours to get a dead battery to take a charge. I ended up replacing my battery after 3.5 years after similar problems, but if it was only a year old I may have tried harder. ($180 from the dealer, not installed)

This is from a Toyota training manual regarding the 12V maintenance free battery:

“This battery is very sensitive to high-voltage. When charging the auxiliary battery you should use the Toyota approved charger, because a standard battery charger does not have the proper voltage control and may damage the battery. If the approved charger is not available you may use a trickle charger if the amperage is kept below 3.5 A.â€

It also recommends removing the battery from the vehicle during charging, but says it is safe to jump-start the Prius from either the battery or the jump-start terminal under the hood.

The battery has a warning label on top that indicates the maximum allowable charging current. If I needed to charge the battery, I would just set my charger to the 2A position, or else use a lab power supply set to 13.8V and with the current limited to the max current per the battery label.

The suggestion to remove the battery from the car is for safety reasons - in the event that the charger does not sense the battery is charged and reduce current accordingly, the battery might overheat or explode. This is a relatively low-probability event, though.

At minimum when charging the battery, the negative cable should be removed so that the Prius electronics are not exposed to the charging voltage.

If you are still in warranty for the 12V, tell the dealership you want a new battery. Be forceful. Bad batteries do exist on this car. I had mine replaced under warranty (free)......then let the dealership investigate for a drain. It's relatively simple, an ammeter in series with the battery. They may not be capable of doing it tho.

And after you get the new battery get into the habit of *always* locking the car, no matter where you park it or for how long. If you have not shut the car OFF or have left a door or the hatch open (any of which can drain the 12V battery in a few hours) this will give you a long warning beep.

In case people read this thread (and no others) before jump starting Prius:

If you connect the external cables wrong (backwards, pos-to-neg), you will kill your Prius. Maybe the $100-dollar way, or maybe the $1000-plus way. Either way, you won't like it.

When connecting Prius to external power, be completely sure that you are doing it correctly. Thanks.

Patrick

Any good modern automatic battery charger is already voltage limited. I know my VDC tender units are completely safe, I checked a large electronic automatic Schumaucher I have and it states 14.8 vdc max

Driving around with a chronically undercharged battery will do it more harm than one charging session with a bit too much voltage

jay

If I were to go on vacation for three weeks would it be ok to use a float charger on the 12 VDC battery without disconnecting the neg. cable?

good heads up

I have an older model of this VDC Battery Minder on all of my equipment

 12 Volt-1 Amp  Charger and Maintainer

I'm even in the habit of plugging in my Prius overnight. Four years now, the 12 vdc battery is very strong. When I power up, the auto headlights barely flicker when the coolant transfer pump runs

I have the harness connected directly at the 12 vdc battery. Once it tops off the battery, it automatically cuts the charge current and enters a maintenance mode

GOOD POINT

Just in case anybody is wondering how you know that you have connected the battery backwards. You will get a tremendous shower of sparks, accompanied by heat hot enough to burn and mark your hands. And possibly some melted wire. Plus voltage just loves to go to ground with absolutely no resistance inbetween. You also may put the Prius totally out of commision. Stay aware of the polarities! One good thing 12VDC and 30-50 amperes probably will not kill you.

Hello Slearner...
Stop...do not touch your car. Read my post of blowing up the inverter. Noone told me to have the car towed in. Now I get all kinds of advice as to why didn't you have towed in right away. If you damage your car with the jump, you will void your warranty. Again, read my post of June 5th...I blew up my inverter....lots of good posts there...but all leads to a costly lesson for me. Maybe we should keep intouch though incase we can find a lot of other people who had their 2007 Prius die. That was my first question.....why did it die anyway...it is only 1 yr old. Would appreciate a post from you on my thread so I can have your story on my topic. And if you would refer any other who have this same problem, please let me know about them or their thread title.
Thanks much....signed "no warranty for me and a big bill....over $5000 with the tax."
Ginny

I didn't know that a battery connected the wrong way (polarity wise) could cause such damage, for that reason I'd recommend a charger that could be connected permanently to the battery which means that it shouldn't drain the battery when it's not plugged into AC. I own allot of chargers and only two I have are like that and only one I'd recommend is a linear type 1.5 amp Patco, the other one is a 4 amp switching type that once managed to blowup a normal wet cell battery I had in a diesel truck.

The manual recomends a charge rate of ~2.5 amps. The Prius 12 volt battery is tiny and excessive charge rate will kill it. The reason to remove the battery from the car is to allow it to vent explosive hydrogen safely.

The amount of ignorance and misinformation about batteries is staggering. If anyone is interested this is a good link about how batteries work and last. http://www.batteryfaq.org/

As we know in the solar business, more batteries are murdered than die of natural causes!

As to destroying the inverter by reversing the polarity of jumper cables. I would suspect that this is possible for a number of reasons, but one would think that Toyota would be smart enough to build in reverse polarity protection. It isn't hard to do.

Icarus

In addition, you can (I know, I have done it!) explode the battery and shower yourself and others with sulpheric acid. If you don't know what you are doing don't F**k around with batteries!

The 12 volt DC will not kill you, won't even shock you, but the other consiquenses are severe,,,including blindness!