Dead 12V battery? Here's a quick way to restart

Blair, you are correct that a relatively small source of 12 volts as a 'booster' will get Prius started, if your Prius (little) battery is low. Eight alkaline D-cells connected in series (even 10!) won't do it though; I know because I've tried. Others have reported success with the powerpack from cordless tools. A 6 amp hour sealed lead acid battery (about the size of a brick) certainly will work, and you may go smaller from there according to your own experience.

Anyone who does external 'jump-starting' of the ePrius lectrical system, please be extra-extra careful to get the polarity correct. Risk of major damage if you do not.

Evan, I do not agree that a depleted Prius 12 volt battery can be fully recharged by its electrical system in a matter of a few minutes. I really could not quote the time but as Toyota specifies a charging rate for that battery as 3.5 amps max, it could take quite a few hours. But you are correct in the sense that the only goal of 'recharging' the car in this way is to have enough power in the 12 v battery to perform the next 'boot-up'.

 

<div class='quotetop'>QUOTE(efusco @ Dec 28 2006, 01:43 AM) [snapback]367558[/snapback]</div>

Sorry Evan, but that's BS.. The 12V battery *is* charged by the HV through the converter, but the process is definitely *NOT* a quick one.. Even at the boosted ~14V level, the charge current available to the 12V battery is quite limited, and that's deliberate. I recently designed a lead-acid charging and maintenance system for a telecom application complete with current limit function for charging dead batteries (ie if the generator option was not available and the system had to run to "empty" before power was restored), so I do have some experience dealing with batteries and charging systems.. Without a charge limit function, a dead battery will basically pull whatever current that a power supply can give them as soon as the main power comes back on, up to hundreds of amps if they can, which, assuming that they don't pop the breakers right away, leaves nothing for the electronics systems.. What you really want is to distribute the available current so that the electronic systems always have priority (because you want service back as soon as possible) and being able to deliver a charge to the battery at the same time and the simplest and most elegant way to do this without having to build in a separate charging circuit, etc is to hard limit the voltage being output by the power supply and monitor the battery current through a shunt- the electronics will function fine, but the limited voltage prevents the 12V battery from pulling too much current. This necessarily increases the time it takes to charge the battery, and on a Prius, it really does take quite a while and you're talking hours of driving vs. minutes to get back to a full charge; just a few minutes of driving will leave the battery still mostly dead and prone to sulfation damage, not to mention the higher probability of requiring another boost if you leave it a long time.. Your best best is to put a charger on the battery as soon as possible..

It's my contention that the main reason for so many dead 12V Prius batteries is not the small battery, but mostly the limited charge rate- I'll bet that if you went around and broke the seals and pried off the caps and sampled the electrolyte on Prii, that you'd find a large proportion of them running around constantly at a partial charge.. This limits the amount of time that they can sit around simply because the battery is not full, but also, being less than fully charged shortens the life of lead acid batteries significantly- these batteries like being fully charged all the time, and even sitting in a partially discharged state can lead to sulfation and reduced battery life, although I also believe that the lack of a "topping charge" by the Toyota system also contributes to this.. I've put a 15W crystalline solar panel (vs. those cheap amorphous things which are much less efficient) with a simple charge controller on my car to ensure that the 12V battery is topped up as much as possible

 

Likewise I've always had a problem with the tone of your posts, and perhaps you don't intend it that way and perhaps the majority of readers don't perceive it that way, but my own perception of your posts has always been: "Thus saith the high and might Evan Fusco, M.D., Moderator of Priuschat.com"- perhaps it's your training as a doctor to never sound unsure, but seldom do I ever read "I believe that..." or "It's my opinion that.." from you. Quite the opposite, it's always a statement of fact, sounding as from an incontrovertible authority, even when you turn out to be incorrect.. I will not apologize because what you posted originally was untrue- Tochatihu has posted the Toyota spec of 3.5A max, and for a totally drained battery of around 35 Ah, this will take at least 10 hours to reach a full charge. Even your latest post is not really accurate- a few minutes at 3.5 A, will get you 3.5A * 5minutes=292 mAh, or about 1% of the total capacity of the battery, ie, it's still dead for all intents and purposes. If you stop the car and leave it after only 5 minutes of charging, the battery will support the electronics for about 4-5 hours before going dead again.

 

<div class='quotetop'>QUOTE(Blair @ Dec 28 2006, 12:40 AM) [snapback]367850[/snapback]</div>

Hi Blair
Could you explane a bit on how you opened the hatch from inside!

 

I too have read Toyota's specification to not charge the 12V battery at a rate greater than about 3A.

However, the DC-DC converter is capable of outputting at least 80A, and there is no isolation of the 12V battery from the main 12V feeds in the car, or from the DC-DC converter.
Unless they are relying on the small but finite resistance of the main 12V line going from the battery at the back of the car to the front, I don't see how the current to the battery can be limited.
There is a white wire fused at 5A going from the DC-DC converter to the battery, which could be a sense lead. Another lead from the DC-DC converter is fused at 100A. The fuse at the battery end is 120A.

You probably could get alkalyne batteries to fire up the car, as long as you don't trigger the accumulator pump to activate. As you know, you have to press on the brake to get to READY. It is possible, but very tricky to press the brake just enough so that the HV ECU senses the push, but not so much that you trigger the accumulator pump.

 

<div class='quotetop'>QUOTE(c4 @ Dec 28 2006, 10:28 AM) [snapback]367646[/snapback]</div>

Nowadays, I am not driving my 2002 Prius very often, and I'm experiencing a lot of problems with the battery even though a new one was installed by my Toyota dealer in May of 2006. (It was an improved replacement.) It has died several times in the past two weeks, and I've used a portable battery to start it. On New Year's Eve, I drove the car for about an hour from Rockville to Baltimore, parked it in a parking lot, and the next morning, discovered someone had broken the small rear window and had perhaps triggered the alarm as the battery was dead again. Fortunately there was no other damage or loss; the culprit didn't look like he got into the car.

I will be bringing the car into the dealership tomorrow as I'm concerned about the battery and this needs to get fixed in order for the glass window to be replaced without a lot of hassles for the repairing company. Hopefully the dealership can condition the 12V battery to get it working well again and perhaps also see if there is a short somewhere. However, since I do not drive the car very often (I no longer commute to a job), I'm wondering what I can do to keep the 12V battery charged. I have a garage, so a solar charger would not be practical right now, and for now, I could take advantage of the AC outlet. I do plan to move permanently to another location where I will not have a garage and where I might be able to use a solar charger.

I also wish that I could deactivate the alarm when the car is in the garage as I suspect the alarm is a major cause of drain on the battery. For a 2002 Prius, is there any difference to the battery whether the doors are locked or not?


Dana
Rockville, MD

 

A small AC-powered battery maintainer that has some simple circuitry to detect when the battery reaches full condition and stop charging is exactly what you need... Most of the full-sized CPU-controlled smart controllers also have a battery maintainer, but many won't work properly due to the load from the vehicle electronics.. This way, you can keep the battery topped up even if you leave your vehicle for months at a time (in which case you might want to also consider gas stabilizer and other similar things)

 

<div class='quotetop'>QUOTE(c4 @ Jan 3 2007, 10:50 AM) [snapback]370082[/snapback]</div>

Thanks, c4. I found out this morning that the starter battery was still dead despite the hour-long drive from Baltimore to Rockville on Monday. The dealer is attempting to charge it up right now but I suspect the problem is more severe than just needing to be recharged.

Would you mind sharing the specifics about the equipment that you use to keep your battery charged up? I will be interested in using solar solutions when I no longer have a garage. I'll be on a houseboat and quite far from the parking lot, so it would be a hassle if the battery dies out there again.

Also, I have a Xantrex portable battery--specifically an XPower Powerpack 300. Not sure which specifications to share, but the internal battery capacity has a minimum of 17Ah and 200 CCA. The DC Power Socket's maximum continuous load is 12 A with automatic reset. Could this be used with a charge controller to charge the starter battery (mine is the special Panasonic battery with 356 CCA that was described in the Technical Service Bulletin EL014-03)? (The Powerpack can't be connected to the AC outlet and charge other devices at the same time.)

Dana
[email protected]

 

Hi ShelbyN

Don't have my Owner's Manual handy, but I do recall that a diagram and instructions for opening the hatch when your 12v battery is depleted is included in the Manual. It's not easy, though... you have to lower the back seat rests and crawl into the cargo space, remove a cover behind the hatch locking mechanism and actuate a small lever.

I agree with some other comments that another "key slot" [like the driver's side door] would be a great deal better solution... Toyota saved a few dollars... :mellow:

 

<div class='quotetop'>QUOTE(Dana 2002 @ Jan 2 2007, 07:44 PM) [snapback]369769[/snapback]</div>

I use a $15 Harbor Freight float charger to keep the battery up on my "pleasure vehicle" in the garage. It floats the battery at ~13 volts, so that it doesn't overcharge it, and I have had ZERO issues with starting the car since putting the charger on it.
Its on sale now at 1/2 price:
Harbor Freight Float Charger

 

<div class='quotetop'>QUOTE(keydiver @ Jan 4 2007, 04:11 PM) [snapback]370942[/snapback]</div>

Thanks, keydiver, but I've heard the battery should not receive more than 3 amps, and I couldn't find anything about this on the operating instructions. The instructions also say the battery should be removed before being charged.

Perhaps my best bet is to disconnect the battery if I'm not going to drive the car for a while, and drive instead of taking the Metro

Dana
Rockville, MD

 

I have several things to ensure that I can always start my car:

First off, a 15W crystalline solar panel in the back window- both the wattage and type of panel are important if this is the route you are going: to begin with, you lose at least 30% of the panel's output putting behind Toyota's solar-absorbing glass, and you also have to take into account how much sun the panel really gets- 12 hours of daylight doesn't necessarily mean 12 hours of full power output: you only get full output for a few hours, and partial output for the rest of the day, and if the panel is in a car, it's even less because the car itself blocks the sun for part of that time.. Because of this, my quick calculations show that you really need at least a 5W panel for any meaningful charge if the panel is inside the car behind the windshield. Secondly, the common type of panel available today is the low-cost thin-film amorphous type- these are identified by the smooth, featureless purplish/brown color. Amorphous panels are often claimed to have "revolutionized" the solar power industry because they can be less than half the price of a comparable wattage crystalline panel (thick slices of silicon that are blue-black and have obvious criss-crossing crystalline formations visible on the surface), but the other side of the equation is that although amorphous panels are much cheaper, they are also very much less efficient, so a comparable wattage is also much larger: I started out with a 5W amorphous panel, and switched to a 15W crystalline- the 15W panel obviously gives 3x more output, but is actually an inch smaller all around than the amorphous 5W panel; by comparison, a 15W amorphous won't even fit sideways in the car.. The other issue is that amorphous panels tend to lose as much as 50% of their output due to aging within 6 months of exposure, ie, a 5W amorphous panel may become only a 2.5W panel in half a year vs. crystalline panels which retain 80-90% of rated output for 10 years or more (mine has a 10-year, 90% output guarantee).

With my 15W panel, I have very good confidence that my battery will remain topped up in virtually all circumstances.. I've left the car for 4 weeks without issue (but I also don't have the extra power drain of SKS or anything like that either)..

The second thing I have is a larger battery- I don't know the exact capacity as the replacement is an actual car starting battery with CCA ratings vs Ah ratings.. The battery is a Honda Civic battery which is the same depth, about 1/2" taller and about a inch longer than the original (the mounting tray has to be modified a bit), and it is even available with the reversed terminals (positive on right) like the Toyota battery. The replacement battery is also a true AGM battery without any free liquid unlike the Toyota battery which you can hear electrolyte sloshing around in, so there is much less worry about sulfation, etc..

Third, I also keep a 12V 7.2Ah "booster pack" in the trunk- I've never had to use it as a booster, but the built in work light is quite useful for other things..

Lastly, I've got a selection of battery chargers- a couple of old "dumb" chargers (basically a transformer and a rectifier that allow the battery to "self regulate" its charge), and a couple of "smart chargers" with variable rate charge, desulfation, test and maintenance modes.. If the battery were truly "dead", I'd disconnect the ground from the vehicle and allow a full charge from any of these chargers (disconnecting from the vehicle is most important with the "smart" chargers because if you leave the vehicle electronics connected, the small drain tends to fool the charger electronics into thinking that the battery is never full, so it keeps charging indefinitely, or that it is bad (shorted cell), additionally, if one of these smart chargers ever decides to go into desulfation mode, you probably don't want the 16+ volts that they use to break down teh sulfation applied to the vehicle electronics.. In fact, if you want to leave the battery connected to the vehicle, it's probably best to use an old style "dumb" charger instead.. I try to connect the smart charger at least once a year, whether needed or not, 1) to ensure the battery is topped up and 2) to allow the diagnostics to see if the battery needs desulfation or any other maintenance.. My original Toyota battery was actually quite badly sulfated when I replaced it (bulging case, reduced capacity), but the new battery has been in place for 3 years this year and is still fine.

 

c4,

Where did you get your 15 watt crystalline panel? Do you use a charge controller with it?

Wayne

 

I've read the posts on this thread and I think you guys can answer my question(s). I bought a 2005 Prius today. It was $800. 183K. It has issues, but I don't know how many. I bought the car thinking it needed a hybrid battery and a 12V. But when the car was unloaded from the flatbed, a HUGE puddle of oil was under the Prius on the flatbed. Anyways, to get it into neutral to tow, I used a jump pack on the rear 12V battery. My jump pack is old and isn't very powerful. It dimly lit the car and I was able to get it into neutral. The car will not get to the point to say "READY" and I don't really want to start the engine yet. With the 12V battery hooked up, the display screen showed the hybrid battery at 4 or 5 bars. Once loaded on the tow truck, I turned my battery pack off. I also "thought" I turned the car off too. When we got to my house, I turned the jump pack back on to put it in neutral again and the hybrid battery displayed the hybrid battery as having 1 bar. Trying to figure out how it lost it's power, or maybe the 12V battery didn't measure it correctly the first time. I can tell that the Prius has been setting for a long time. Thick cob webs built up in the door corners. Leaves and tree debris all over the car. So my question is, how, without running the engine, can I charge the hybrid battery? If it's been sitting for a year, it could be that is is dead as well. Let me know. Thank you!

 

A charging system from "Prolong" is commonly mentioned around here. I don't have any personal experience with it.

If you're near a university that holds old-equipment sales, you can sometimes pick up an electrophoresis power supply for cheap and make that work if you know what you're doing. But anything that wasn't designed and built to give a controlled, limited charge to a traction battery, you've got to watch like a hawk.

 

Since you’ve bought a project, the fun begins.

The hv battery sounds like it is done, but the 12 volt is also spent. If you have a puddle of oil on the truck, I’d start looking for the source of that issue as that is something you can do to determine if the engine can be saved.

If that is as simple as a loose drain plug or oil filter, I’d then begin to determine options for the batteries. At minimum you’ll need a multimeter. Read up here on how to work around high voltage and ensure you know how the orange plug works in all three steps.

Good luck and keep us posted .