Jump starting our dead Prius

It is not necessary for the donor vehicle's engine to be running, as the Prius only needs ~30A or so for a very brief period. Just make sure that you have battery polarity correct: positive to positive; negative to negative.

Once you get the Prius running, it needs to remain READY for at least 8 hours to bring the 12V battery back. Ideally you would hook up a battery charger, but if one is not available then you can leave the car READY for an extended period to recharge the battery.

After allowing the battery to charge for that period of time, if the car has another no-start incident then you can assume the 12V battery will not hold a charge and needs to be replaced.

 

What Service!

 

When I parked my car at the airport last week, the idiots killed the 12 volts battery. I jump started it, and drove home, which took about 40 minutes. I turned he car off. It has been running OK ever since. What is the reason for 8 hours? The battery is not trickle charged.

 

Lead-acid battery lifetime is a function of how deep the discharge by how long it is kept from recharge, (and the number of these cycles) so the sooner you *fully* recharge it, (within reason) the longer it will last. If you jump it, drive 40 minutes, it might be charged enough to start the next day, but will continue to sulfate because the charge was not finished.

Patrick's recommendation is good, because you assume a near totally flat battery if it won't start, and because the Prius charge system isn't a 3-stage, the last bit can take a long time.

The other option is to get an intelligent charger, such as one of these that will fully charge the battery without possibility of damage (overcharge). Be sure to set it for AGM. *Never* use an old style "dumb" hardware store charger on the Prius battery if you want it to last.

 

As implied above, the Prius charge system is not a quick-charge type. It runs at a nearly constant voltage of about 13.8-14V. This won't rapidly charge the battery, which is why the 8 hr time period is often used. This is particularly important in winter, as a lead-acid battery requires a higher voltage to charge fully, and the Prius charge circuit doesn't have temperature compensation built in.

If you just use the car for 40 min a day, and had to jump start it at the beginning of the week, the battery would probably suffer some sulphation damage over the week. It would probably still work over the week, and you might not notice the damage for a few years, but it will still happen.

 

There is something definite amiss, either the battery is deficient or the charging system is deficient. Interestingly, no matter what battery I install on the Prius ( new, older, wet cell, agm ) they all revert back to the 12.2 to 12.3V level on the self diagnostic check. A DVM also concurs with these readings. This is after charging them on a bench from 3 days to a month at about 3 Amperes. Wierd!

 

You can't contend the Prius charging system is inadequate without testing it. What is the voltage at your 12v battery when the car is Ready after a few minutes?

What temperature are you making these tests?

 

I am a consumer, not a scientist, so I can contend anything sensical or non sensical! This is a forum where we literally throw ideas around, Sacto temps are about the same as Berkley. And these observations have been made over a period of six years now. I would estimate at least 300 to 1000 battery complaints on PC alone. This figure can probably be multiplied by 10, at least for the other Prius owners. There are also PCers who join a battery thread when the subject comes up. So possibly my numbers can be increased again by a factor of 2 or 3. All the Engineers associated with the Toyota Prius certainly have the knowledge to speak with authority on the inadequacies of the 12 Volt battery. But, they are all as quiet as a mouse. NOW........there could be a very good reason why Toyota has limited the self charging ability of the car, perhaps 12 - 12.5 is the ideal range for Prius. Your contention???

 

He said no such thing.

 

He said nothing, but he typed "Deficient". With either word, you still have to test the DC/DC converter before you can assume that's the cause and not the battery.

Most Prius 12v batteries seem last about as long as most other car batteries. The demands of the SKS can be hard on a battery if the car isn't driven much.

While I agree that the addition of a 3-stage charging system would benefit the Prius, it's going to add cost which is probably why we don't have it.

If your battery is healthy (no shorted cells, etc), in ready with accessories off you should see at least 13 volts, and usually more like 14. (depending on battery charge) Once the car is off, the battery will settle down to anywhere from 12 to 13 volts depending on it's age and ambient temperature. If your battery drops lower than this then it's likely bad. If you don't see the car come up over 13v when it's ready, then I'd suspect a problem there.

 

Your findings reflect my exact observation on my 2007 oem battery.
And also my full size car battery thats a few years old in my other car.
Both are very well maintained, never gone flat and see periodic float charges.

And your findings are normal. You must not own another car to compare it to.

Going on my 4th year with my oem battery and its fine. If there was a charging limitation our little batteries would give up the ghost in a matter of months. But there pretty good little batteries. You just can never kill them flat once and you have to drive the car pretty often. Only because there's a standby load on it higher than a dumb car. Not much but its a very small battery and can be killed by parasitic loads for days as in a long term storage.

If you put a charge on a healthy battery thats a few years old using a battery charger or even a float charger over a period of days about the highest you'll ever see it charge to is 13.2 volts.
Thats sitting there with the engine not running after a long charge.
Thats really pretty good. A brand new battery will charge a little better than that but not for long.

Now start the car and run it for a day or so then shut the car off and with a voltmeter check the battery. You'll see anywhere near 12.7 to 12 depending upon how old the battery is. Even though the alternator as in a regular car is applying 13.8 continously. Of course our cars use the Inverter but no difference in charge voltage.

Because even though your charging the battery when the car is in ready your also putting a good running load on it. And most car batterys will not hold that max charge level very long with even a slight load on it.

The most telltale sign of a good battery, short of a full load test is how fast it will take a charge. A prius battery that has been in the car for a few years and has never gone flat and sulphated and with a battery charger on it in the 2 amp mode should charge the battery to 0 amp draw in about 15 minutes. My car has doen that since day one.

My other car with a very heavy duty battery exhibits identical behavior. Its a good thing to periodically charge your car's battery so you can monitor this charge rate because when a battery gets worn out it will struggle to charge up to 0 amp draw quickly.

My 07 oem battery will measure 12.3 volts with my Fluke with the car off and after running around all day. Not excellent but not bad either. Quite normal.

My other car shows the same.

I implore you to hook your battery to a good charger with a 2 amp mode and see exactly how fast it takes to go to 0 amp draw.
Its a good rough estimate of the batteries health.

 

I think hands-down, the biggest source of confusion/frustration on the Prius is the 12v battery. Because it is not called on to actually crank the ICE as in most cars, you don't get the same "slow crank" warnings when it's on it's last leg. One cold morning it just won't go ready with no advance warning. It's also the cause of numerous strange and seemingly unrelated problems. I bet millions have been wasted at the dealer service dept!

The absolute best way to test the 12V battery is to use a professional transconductance tester. Most of these are made by a company called midtronics, but a few other companies such as OTC make them. This is what the dealer should have, also many battery stores and auto parts suppliers have them and will be happy to come out and test your battery for free, just make sure they choose the right size before testing. (IIRC it's 37Ah for the SKS equipped Prius)

These transconductance testers measure the true capacity in seconds regardless of the battery's state of charge. There is no way to accurately determine capacity with a volt meter, but you can usually spot a truly bad battery this way.

Last year I went on a search for one of these pro testers and found they cost crazy amounts of money ($800 for the cheapest model new!). At that point I gave up my search, but was pleasantly surprised a few months later when someone I know offered me a brand-new OTC transconductance tester for $150. He had 5 of them, so I bought all 5 for $500; a screaming deal! They are Exide-branded and are normally sold for $1000 to Exide dealers. They will test from 7Ah to 250Ah batteries (will also allow input of CA/CCA for car batteries where Ah is not listed).

I've sold 2 of them to my friends, and I still have 2 left if anyone here is interested. $150 and I'll cover shipping.

Update: Both Testers have been sold!

 

The cheaper, one-size-fits-all (sub-$500) conductance testers can be fairly hit-or-miss.

And it looks like the tester that you are offering to sell for $150 sells for about $80 new:

http://www.superiorserviceandequipment.com/Brochures/BatteryTesters/ACT2/ACT_Tester.htm

By the way, Toyota dealers use something a little more specific: http://toyota.spx.com/pdf/GR8.pdf

 

Wow, I guess I didn't get as good a deal as I thought!

The Toyota thing is a combination Transconductance tester and charger in one unit. It's made by the same people that make the one I have.

I can recommend the ACT even if you don't buy one of mine, they work very well and are settable from 7Ah to 250Ah, so not "one size fits all".

 

Notice that those on the web site jk pointed at aren't new but refurbished, fwiw.

 

Good eye; I didn't catch that. The ones that pEEf bought may be refurbs, as well. However, I have a hard time believing that they once sold new for $1000. I certainly hope no one bought them for that much.

 

deleted... refurb already noticed...

 

Good tools tools are pretty pricey. If it's a highly technical tool, then the cost really climbs! I recently scored a Fluke Scopemeter off of craigslist for $350 in like-new condition. Fry's has the same model in stock for $1300.

The bill of materials in something the ACT tester is likely under $40, but because it's a limited market and usually has a large handful of patented technology, there is a good markup.

 

I'm a little late getting back on this. A dead battery should first be charged with a constant current, unitl the voltage gets up to 2.4 volts/cell, then with constant voltage for 8 or 9 hours, then float charged at 2.2 volts/cell. For a "12" volt battery, that is 14.4 and 13.2 volts. In a car, you don't get constant current, and you don't get float charging, just constant voltage, so the battery will not have optimum life, especially after completly discharging it. True, you don't want to keep a lead acid battery discharged for long, but I see no good reason to recharge it immediately for 8 hours. The extra energy required to run the car for that amount of time probably exceeds the cost of the shortened battery life, and for 1 incident, the shortened life shouldn't be dramatic. Of course, if you have a charger, and can conveniently hook it up, then complelty charging up the battery is a good thing, otherwise, I don't think it is necessary, unless you will not use the car for a while, or put enough time on it within a few days to charge it up.