Installing new 12v battery

On our last car I would hook up a trickle charger: positive charger lead clipped to battery positive cable. Negative charger lead to ground (car body or engine bare metal). This was a very low 0.5 amp motorcycle trickle charger, something you can pick up fairly cheap.

Disconnecting the battery, the memories were retained ok.

With the Prius battery in the hatch the circuit is a bit more "circuitous", but I think it would still work, ie: hook up trickle charger positive (red) lead to the red-capped positive jumper plate in fuse box, and negative (black) charger lead to ground. Doing this, I believe you still are supplying a light amount of charge, and memory will be maintained when you disconnect the 12 volt.

Always attach make the negative (black) connection to ground last, and disconnect it first.

 

If you use a charger, you'll need to make sure it will continue to provide 12V to the car when the 12V battery is disconnected. Some chargers in the interest of safety will cut power if they detect no voltage or incorrect polarity from the 12V battery.

If you hook up jump cables to another car's 12V battery, be very aware that you must not short the positive terminal connector of the Prius' 12V battery to ground when disconnecting it since that connector remains live due to the power supplied by the donor car's battery. If you short that connector, you will at minimum create a big spark which will probably be scary to you, and may blow the 100A MAIN fuse depending upon the condition of the donor battery and jump cables.

 

A portable jump start pack is the ideal tool for this job. They are incredibly handy -- I used mine to resuscitate a big pickup truck battery that was down to 2.5V, so far down that neither the Battery Minder nor the cheap Exide 6A charger would deliver any current. Sorry that you lost your settings, just be sure to do the power window initialization.