12V battery empty

^ Ouch. Warming here, currently right on freezing point: 0C, 32F. It's been cold enough there's a small lake or two that skating is allowed.

 

I thought the Prius does not really use "cranking amps" The Engine is started by MG1 off the traction battery, isn't it?
Still learning...

 

It may not use the battery to run a conventional starter, but still I think a cca tester gives an insight into the battery's viability. Most batteries start life above their rated cca, and by their "twilight" cca will have dipped below the rating.

I'm really out of my depth too, just my take on it.