jump start battery capacity?

This is probably up to the task (short 20 amp or so surge then just a small load to get the electronics running), a carbon-zinc battery has limited shelf life so make certain not to get one. This one seems to be an alkaline battery which would have a 5 year shelf life so it is a reasonable choice.

I just remember to recharge my sealed lead acid jumper (with an air compressor - very useful) periodically.

JeffD

 

This would work. It only needs to bring up the electronics.

I use a sealed nickel hydride battery $20 with a diode and switch. Tie in at the console power adapter (power mod always active). Driving charges the extra battery, doesn't drain it. Dead battery, Flip of a switch and I'm ready to go. Stores well under an empty space under the center console, switch in the console. Already used it once.

Walmart (not promoting) has the same Lantern Battery for less. RadioShack just puts their name on Duricell or Eveready.

 

What makes you think you will need it? A much more useful device is the one Jeff mentioned. A sealed lead acid "boost pack". They come with lights, air compressors, etc. Bonus, it will let you boost other cars when asked (NEVER boost another car with the Prius battery!). Charger is built in. Just plug it in every month or two and you're good to go.

And if you get the one with the air compressor it's MUCH more useful, because maintaining tire air pressure is the single most important thing you can do for safety.

 

If a boost pack floats your boat, thats fine. I wanted something small out of the way, just the battery backup no maintenance (charge in the house, remember it, tote it back to the car).
Charger built in...That means its at home when you need it maybe in the parking lot?
I've had two boost packs. Both the battery and air compressor failed after a year. They were cheap. Most places local to me have free air check. Let someone else get their hands dirty. So far only need I had for tire air was in the 5k rotate with oil.
While the spare battery isn't a nicey thingy, Its handy when the main battery is dead.

 

Be aware, whatever you choose must supply a 50 Amp half second pulse with the voltage not dropping below about 10V. So good hefty terminals, reasonable wire sizes, etc. are needed. I made a boost cable using #10 "trolling motor" wire and solid copper clips. The dead 12V battery won't have much effect, as it doesn't draw much from a 12V supply. Especially from the boost terminal.

 

I guess that the first-mentioned is too small. Two 6-v CZn lantern batteries in series would not do it for me. That was probably about a 2 or 3 Ah string. However, some chemistries with very low internal resistance (such as NiCd) can manage with very small Ah capacity.

The main thing is that when any external DC is connected to the Prius, the polarity must never be reversed! I always say that.