Toyota Prius Hybrid.

[Eric H]

A dead 12V battery shouldn't affect the traction battery at all but the 12v battery is required to start the car since it runs all the electronics.

Leaving the rear hatch ajar is the most common cause of Prius no starts at my work, we have to jump start them often for this reason but it's never caused any other issues.

I don't know why Toyota doesn't have a Battery Saver relay to prevent this problem, or some way to use the traction battery to give the 12v battery a boost.

I recently had to fix a couple Ford Escape Hybrids at work, they had sat for eight months so naturally the 12v batteries were dead, in addition the traction batteries had discharged to the point they wouldn't start the engine.

How to fix that? Turns out the Ford (at least on the older models) had installed an emergency button that would charge the traction battery from the 12v battery enough to start the engine.
Press the button (with a good 12v battery) and eight minutes later the vehicle starts, provided of course the traction battery hasn't been discharged to the point of ruin.
Eight months was cutting it pretty close, they were down to less than 30% charge at that point but they recovered.

[Ed in Tx]

Originally Posted by Eric H

Leaving the rear hatch ajar is the most common cause of Prius no starts at my work, we have to jump start them often for this reason but it's never caused any other issues.

I don't know why Toyota doesn't have a Battery Saver relay to prevent this problem, or some way to use the traction battery to give the 12v battery a boost...

That makes no sense! Even my '02 Trailblazer times out after 20 min and automatically shuts off all lights interior and exterior if a door or the rear liftgate isn't closed all the way. All done in the body control module.

[rca2000]

My 1986 Riviera ALSO had a battery saver feature--that would cut off any lights left on--after 10-15 minutes or so. my van I have now--a 2001 Chrysler T&C--also does.

[dieseljeep]

Originally Posted by rca2000

My 1986 Riviera ALSO had a battery saver feature--that would cut off any lights left on--after 10-15 minutes or so. my van I have now--a 2001 Chrysler T&C--also does.

I thought, for sure this Toyota had it as well. When I went into the garage, the next morning, the light was on.
This car has all kinds of tricks. Keyless start and entry, back up camera and climate control. All kinds of options, that spoil you.