2004 will not start/post with brake pedal.

I don't think the hood is a proper ground, you should use the strut tower nut next to the positive connection on the prius.

Also doesn't the good battery (bmw) have to be fully connected? Positive and negative terminal on battery

 

I'm confused by your connections. The prius has the (+) cable connected to the jump point under the hood with the (-) cable connected to hood latch (unusual)

But more than that, what is the red cable (+) connected to on the BMW? I'm not familiar at all with BMW construction. Is that a jump point also? The (-) cable appears to be connected to the battery. I'm not familiar at all with BMW construction

 

if you can get to the battery, attach it to the battery terminal itself. If it's hard to get to, maybe you can just flag down a fella that will help with a jump start?

 

Yes, good battery fully connected positive and negative. Dead battery gets positive and ground.

 

The Prius battery is in the right rear of the trunk/hatch area. But the jump points you have for the Prius is correct, just the ground may not be correct (as the hood is aluminum). Try grounding on the strut nut and I think you'll have better contact.

To get a battery reading, a simple tool would be a multi meter

 

This is one of those cases where the OP should have read the owners manual of both cars before attempting a jump start.

It's time for a new one.

 

The 12v battery you have not is probably toast, but you can try to charge it and see if it'll hold the charge. If it won't hold the charge (checking after it sits for 12 hours after charging), you'll need to replace it. Not holding charge would be fully charged 12.9v down to low 12v or less overnight

A fully charged battery will be around 12.9v. A still functional battery will be around 11.5v (meaning it'll still start the car). You really want to charge up a battery that reads around 12v or less, as the car probably won't be able to fully charge it at that level.

 

If your jumper cable alligator clamp was sufficiently small so that it would have a good connection to the threaded stud and nut, that would work. However most clamps are too large, hence the flat terminal above that is intended as the dedicated positive terminal jump point.

The need to use the terminal "several times" is not good. That implies the 12V battery is dead and needs to be replaced; or the car is driven very lightly and a battery charger or battery tender should be used to keep the battery charge up.

 

It is risky to use the Prius as the donor for a jump especially at the dedicated jump start point because the 120A MAIN fuse is inline and might be blown depending on the condition of the recipient vehicle. If you must use the Prius as donor, connect directly to the battery in the hatch, then you are only risking the battery itself.

Not to mention the Prius battery is marginal at best and not intended to provide starting current for a traditional gasoline engine starter motor.