Jumpstarting another car with a Prius...

Not recommended. You should ask a friend, relative, or neighbor to stop by with their car instead.

The portable jump starter should work fine as long as the Accord's battery can be jump started. Sometimes a battery just dies and cannot be jump started. Do you have an Autozone or Advance Auto close to you? They'll test your battery for free.

 

Yes, you can try to jumpstart the Accord with the Prius. This is not recommended because if you fail to correctly execute the procedure, you will damage the Prius and end up with two non-functioning vehicles.

Any reasonable portable jumpstart device can be used. If you are going out to buy such a device, typically it requires an overnight charge before it can be used. Such a device, fully-charged, will immediately start the Accord assuming that the vehicle is in good working order (other than having a dead 12V battery.)

If you are confident that you will not screw up the Prius jumpstart, then here is the procedure:

1. Make the Prius IG-OFF.
2. Find the Prius 12V battery hiding in the right-rear hatch floor and remove the hatch trim panels sufficiently so you can access the 12V battery positive terminal.
3. Attach the positive jumper cable (with red handles) to the Prius 12V battery positive terminal and to the Accord 12V battery positive terminal. These terminals should be marked with a red plastic cover or a + symbol.
4. Attach one side of the negative jumper cable (with black handles) to the Accord 12V battery negative terminal. Attach the other side of the negative jumper cable to a substantial piece of unpainted metal bolted to the Prius body. For example, the aluminum bracket holding the brake power supply to the hatch floor.
5. Try to start the Accord now. Once it starts, disconnect the jumper cables and do not allow the positive and negative cables to meet while one or both sides remain connected to a 12V battery.
6. If there is any doubt about the condition of the Prius 12V battery (for example, the Accord takes a very long time to start which makes you think the Prius battery is in a discharged state) then apply a battery charger to the Prius battery overnight, or else make the Prius READY and leave it that way overnight so that the 12V battery has a chance to charge up.
7. Put the Prius hatch floor back together, and the car will be ready for use.
8. Leave the Accord running for a few hours to give its 12V battery a chance to charge up, or use a battery charger on it. Do not think the Accord 12V battery will be restored after 15 minutes run time.

Good luck.

 

Correct. There are at least three reasons that you should not use the dedicated jumpstart terminal located in the main relay/fuse box near the inverter:

1) That terminal is intended for the Prius to receive a small amount of 12V power needed when the Prius is being jumpstarted, and is too small to provide the power required to start a conventional gasoline engine.
2) Even if the terminal was sufficiently large, the starting battery current would have to flow through the 120A MAIN fuse located at the Prius 12V positive battery terminal, which risks blowing that fuse. If that happens, then the Prius will be dead.
3) Further, if the Prius is READY when the jumpstart is performed, then the DC/DC converter will be operational and will be delivering power to the 12V bus. The 100A DC/DC fusible link would also be at risk if another vehicle is being jumpstarted and if that fuse blows, then again, the Prius will be dead.

My procedure requires you to connect the positive jump cable directly to the Prius 12V battery terminal and keep the Prius IG-OFF, which means that you no longer have any of those fuses in the circuit. So as long as you observe the correct battery polarity, the most harm you can cause is to the Prius 12V battery by itself.

If you have any concern that the Prius 12V battery is not fully-charged, be aware that using that battery to jumpstart another vehicle may result in the Prius battery dying - which leaves you with two dead vehicles.

So since you currently have a working Prius to drive, the lowest risk approach would be for you to go out and buy a new 12V battery for the Accord, install that battery, and call it a day.

While you are shopping, you might also buy a portable jumpstart unit and plug it in to AC house current so that it is charged up, then you'll have that available for the next jumpstart emergency. Further, it wouldn't hurt for you to buy a 12V, 4A (at least) current capacity AGM battery charger so that you can use that on both cars' batteries from time to time. If they are fully-charged periodically, that will lengthen the batteries' service life.

 

so, sorry, but I am clueless. I hope never to face this, but if I do....

What exactly does:

Make the Prius IG-OFF.

Mean?

 

IG = ignition

Not Ready Mode, not Accessory Mode. Off.
SCH-I535

 

The Prius has four possible operating modes:

IG-OFF (ignition off), where the car is powered off and ready to be locked up. The POWER button LED is dark.
ACC-ON (accessories on), where the MFD lights up but the dashboard lights are dark. This is suitable for playing the stereo assuming the 12V battery is in decent condition. The POWER button LED is green.
IG-ON (ignition on), where all dashboard lights are on. This mode consumes substantial 12V power and should be avoided for more than very brief periods. The POWER button LED is orange.
READY, where the car can be driven. The POWER button LED is dark.

You can cycle among the first three modes by repeatedly depressing the POWER button, without depressing the brake pedal.


The POWER button LED status described above is for North American vehicles. Prius outside NA may behave differently.