Jump-Starting another vehicle with my 2005 Prius

I use my Prius to carry a Jump start pack

 

You may want to buy and keep in your Prius one of these portable jump-starters, which will not only help you to jump-start your own Prius but also to become a good samaritan in jump-starting others' cars (non-Prius & Prius).

I have one in my car, always. I do have a pet peeve with these portable jump starters in that if the car battery to be jumped is really weak, the portable jump-starter needs to be fully recharged (can be done with a USB port and USB cable) before attempting to jump the really weak car battery.

I also keep a solid jumper cable in the back always, since these portable jump starters cannot be 100% trusted, so that I can ask some non-Prius driver to give me a jump, if I get stranded in the middle of nowhere, in a desert or forest.

 

I’m sure people have—in emergencies, one does what one must—but as @Tideland Prius kindly notes...

...and it might be worth reviewing briefly why this is so:

• If the booster cables (jumper cables) are connected with the wrong polarity (positive to negative, or vice versa), at either vehicle, even for a moment, it can do damage that will be costly, or at least tedious, to repair, as many PriusChat threads can attest.

• The 12-volt electrical systems on Prius cars aren’t designed to supply cranking current for a starter motor. The car’s own engine is started by MG1 in the transaxle, using energy from the HV battery.

It’s probably fine to use a Prius car to jump start another Toyota hybrid, battery-electric, or fuel cell electric vehicle, as long as you’re very careful about polarity. If you have to use the auxiliary (12-volt) battery from a Prius car to start a vehicle that uses a starter motor, consider removing the battery from the car first.

 

I occasionally jumped another car from my Gen 1 Prius, before I had a jump pack to use for such things.

I would first get the Prius in READY mode, then just unplug the battery in the trunk (two cables simply plug in at the + battery clamp, same as Gen 2). Then the battery was isolated from the car and I would just run jumper cables from the battery to the other car. After jumping, I'd just remove the cables, and plug the battery back in.

The point of having the Prius be READY first was in case the other car drew off enough energy to drain the Prius 12 volt battery. Instead of worrying if it would still be able to start up the Prius to get recharged, I'd have the Prius already READY, and it would recharge the battery as soon as I plugged it back in.

In old cars with alternators, letting the engine run with the battery unhooked was a no-no, but the Gen 1 Prius converter didn't mind.

I think Gen 2 is less tolerant than Gen 1 of having the skinny (voltage sense) wire unplugged. I don't know if it will drop out of READY if unplugged while READY. If it does, that would make this less practical than in Gen 1.