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Why can't they jump a Prius battery?

I have a Prius, and have had my battery jumped a few times. In my experiences, the guys with the big truck have big cables with big clamps, and therefore have trouble getting a good connection with the small post. The portable jump pack seems to have smaller clamps, so they don’t have the same problem.

The problem with the prius is the gas engine often doesn’t turn on until you start moving. Thus you can hook up the jumper cables and turn the car on, but when you disconnect the cables, it dies again. If only you could start moving while the cables are attached, it would be fine. But that is difficult with the tow truck blocking you in your garage!

I had this EXACT problem, and being an electrical engineer, I was able to find the very simple cause, and fix it easily. Yes, big jumper cable clamps make it difficult, it does not make it impossible. One of the culprits is the fact that the positive terminal connector in the front hood only has ONE metal side and one plastic side. Since jumper cables are made to clamp onto the metal frame of the car or battery terminal, even though both sides of the clamps have copper teeth, often (but not always) ONLY one side is connected to the jumper cable wire. So at random, you only have a 50% chance of the jumper cable clamp making an actual electrical connection on this one sided terminal. It is possible the mobile jump start unit had both sides of the jumper clamps connected or you got that 50% lucky.

Good thing you have that degree. Money well spent.

" . . . even though both sides of the clamps have copper teeth, often (but not always) ONLY one side is connected to the jumper cable wire. "
Right, sure, but the other side that isn’t connected conducts electricity from the side that is.

I don’t see why there’s not an option to use some of the juice in the hybrid pack to revive the secondary battery.
Al that’s needed is a DC-DC converter.

The hybrid pack is so much bigger and it normally never goes below 40%, so there’s enough reserve.

The problem is that the car is needing WAY TOO MANY starting assists. May I suggest that the owner needs to replace the battery in his keyfob assembly? The car won’t start unless the fob is inserted in the key slot. Do not leave the key in the slot when not using the car as it will cause the battery to run down if something is left on. (radio?)
Also, to work around the engine not starting when using a jump battery, turn the A/C system before trying to jump start. The A/C will draw enough current to allow the motor to start immediately.
These Priuses are basically a bit more complicated than the run of the mill Toyotas and require the driver to pay attention to the start sequence.
That said, READ THE MANUAL!!
By the way: NEVER EVER try to use the Main Drive Battery to do anything! The 400 plus volts at high amperage WILL kill you if you touch the contacts in the wrong manner. Even if you could connect to it, you would risk a battery explosion. Maybe in your face.

I have a 2009 Prius and left the dome light for a weekend. Couldn’t jump the battery so I called AAA. The guy who came said he often has trouble getting a good connection to battery lead. He took out an all metal vice grip and connected it to the lead. That gave him a good enough connection so that hooked the cables to the vice grip it started right up.

Let’s say the caller does this a few more times, with a tow truck and with a jumper battery pack. And his observation is correct each time (pack works, truck doesn’t). Is there any chance that trucks use a more complex jumping device with a current limiter? About a month ago, a caller called saying the terminals of his battery melted in when he drew too much current. Batteries will try to provide as much current as it can, even to suicidal ends (conclusion by Tom and Ray as well). Therefore, the jumper pack could provide enough current but not the truck?

Just a thought, I am sure someone will respond saying that tow trucks just jump from their battery and that there is no current limiter :slight_smile:

Yes you can jump start you Prius. The battery for the car workings, ignition, lights starter, accessories, is a standard type 12 volt one with jumper terminals near it’s location. Read the manual!
I will repeat the previous warning,
DO NOT TOUCH THE DRIVE BATTERY TERMINALS! YOU COULD BE KILLED. Unless you have some knowledge of how this car works, take it to a licensed mechanic.
The key fob battery is a good thing to just go ahead and replace due to age.

5 year old thread, why?

I didn’t notice the dateline.
Frank Martinoli

This is incorrect. There is no ‘starter’ on a Prius. The engine is started by one of the two electric motors, using the main (high voltage) battery pack. So if that pack is dead, you can’t jump start a Prius.

I beg to differ.
Yes, there IS a starter. There is an automotive type battery in the engine compartment and there are two dedicated jumper terminals provided.
During the time that I was working at a major auto auction company there were dozens of these cars that needed to be jump started. Nearly everyone on the lot crew knew how to do it. No different than a standard car. Easier than many, actually.
If the drive pack is dead, the gas motor will charge it when it’s running.
Also, if the drive motors are used to start the motor, how would you be able to stay in one spot once the gas motor is started? The electric motors are connected to the power pack and the drive wheels. and the gas motor is connected to the transmission. There is an alternator on the gas motor for charging the battery pack and the automotive battery. (Separate batteries.)
I hope this is a clear explanation.

As I said , I didn’t pay attention to the dateline when I started. But since I have, I thought I’d add my experience to the thread in case someone else has the same problem.
No problem in that for me.

Frank, I never said anything about a starter.

There is a starter.

I’d like to see a link to where I can purchase a starter for a 2013 Prius.

No such thing as a starter for a Prius, guaranteed. “Jumping” a Prius means supplying 12v to the battery that runs the electrical systems like dash, engine computer, that kind of thing. If the 12v battery dies the car won’t start because the control systems won’t work. Sometimes jumping works in that case. But sometimes a really dead battery can’t be jumped, as I learned with my MKZ hybrid, which uses the same overall system as the Prius.

"Also, if the drive motors are used to start the motor, how would you be able to stay in one spot once the gas motor is started?"
You need to look up how Toyota’s Synergy drive works.

I’m stumped for the moment. I’ll look into this and get back to you later if that’s OK.
I found an interface part to the flywheel but, it appears that the unit may be driven by the inverter in some way. Possibly a divider that uses either battery as needed.