How likely is it that a dealership will have a Prius 12v batter in stock?

100% likely,,,,,,,,,,,,,,

How did you find out the Battery was bad, did you get a code for it?

The 12 volt AGM (absorbed glass mat) auxiliary battery in your Prius is a common failure and WILL be in stock at your local Toyota dealer.

NOTE: Do not attempt to Install the battery yourself as there about 3 different Initialization procedures that have to be followed on the 05' Prius and a Factory Toyota "TIS techstream" or equivalent in necessary to perform the initialization.

ADDED: @ The other poster that knows so much,

The C2318 code is a low voltage error (power supply malfunction) code, this code will set when the Auxiliary battery voltage goes down to approx. 10 volts. and If you would bother to look at the Toyota TSB it tells you what Initialization procedures to follow for the particular model!

Any Toyota dealer will have them. They are not hard to replace, many Prius owners have done it themselves. You will have to reset the radio stations and window (it tells how in the manual) if you don't have a way to keep the voltage up while disconnecting the old battery. The only difference with the Prius battery is that there is a vent you need to attach. Also be sure to get the polarity correct.

A dead battery won't throw a code (for the battery) it may throw unrelated codes--and it's pretty obvious that the battery is dead when the Prius won't go into READY mode.

hope you have deep pockets you can buy it cheaper on line but need and expert to install it

before buying one check charging system

they will have it. dont worry