Which battery is which?

[David Beale]

I wouldn't recommend doing this, however (disconnecting the 12V battery while the car is in "Ready"). You loose some regulation of the system voltage. I don't know how much regulation you loose or how much more susceptible the electronics would be to voltage problems, but I wouldn't want to find out. The results could be expensive! I suppose the design had to be done so the system would be ok (in case the battery failed).

The engine is started by the inverter/traction battery. When starting the car you press the brake pedal and the system (brake booster) draws a 1/2 sec 40 Amp pulse from the 12V battery, then you press "Start" and it draws another 1/2 sec 40 amp pulse of power (putting the computers and electronics in "Ready"). After that you will see a current -into- the 12V battery ("float charging" it). The inverter 12 Volt system charger takes over (actually running at 13.8V).

[patsparks]

Never disconnect the battery of a vehicle with an alternator while it is running, you can damage the electrical system Same goes for Prius. The battery may not be providing power but it is a reservoir of electric energy.

Edit, thanks David, I posted as soon as I saw about disconnecting batteries but you had it covered.

[Kidd]

I have to laugh at my ignorance. I originally posed the battery question and received these great responses. Most of which totally blast me out of the water with my next to zilch electrical and auto mechanical knowledge. Regardless of that fact, I am glad I was able to spark some obviously much needed attention on the battery question. Rock on dudes!