Car Talk Prius Question Not Really Answered

It would be really good if she also outlined what else she does while cat-napping, e.g if she leaves something on in the car powered by the 12V battery... I know of one work person who goes out to her car at lunchtimes and reads a book with the fan on full blast and the motor off...

 

Or perhaps she leaves something like a laptop ect. plugged into one of the outlets

 

Yes, suppose this woman leaves the car IG-ON (not READY, where the various instrument panel warning lights are on) and has the ventilation fan running, the stereo on, etc. If the 12V battery is in marginal condition then the battery would be sufficiently drained after 30 minutes so that the car would not start.

 

She may have SKS and not know it, in which case pulling the fob out of the slot would have no effect, true?

As Tom and Ray noted, on those occasions when her Prius won't start Elsie has undoubtedly not shut it off; she has left it in ACCessory or IGnition-ON. The Prius 12V battery is a wimpy little thing, and having been drained a couple of times it's now toast and needs to be replaced. After doing that the simple solution to Elsie's problem is to *leave the car completely ON and Ready* during her catnaps. She should shift into Park, set the parking brake, and lock the doors. She can then sleep as long as likes even with the A/C and the radio on with no harm done until she runs out of gas. Starting with a full tank of gas it would take about an entire day to run out under those conditions. It is extremely important to shift into Park and not Neutral, both for safety and because the car cannot recharge its batteries when in Neutral. And of course this should only be done in a well-ventilated area or outdoors, and not in a completely enclosed space.

 

I have not listened to the segment. I'm going by what's posted above:

If she has her headlights on while driving, then shuts the car off, but does not turn off the headlights or open the driver-side door, BINGO: dead 12-v battery.

 

10 gallons takes roughly 4 to 5 days...

good observation daniel

 

I, too, have not listened to the show, but I think Daniel's come up with a very likely cause of the problem.

 

This begs the questions: How long would it take for the headlights to drain the 12v battery, and how long a nap did she take?

Of course, battery health and SOC are big factors, but I would hope the 12v battery could handle the the headlights for a 20-to-30 minute nap.

 

A pair of 'filament' headlamps should consume about 8 amps (HID less). The capacity of the 12 v battery suggests >3 hours to empty, but any particular battery might get to a no-start level long before that. Especially if the battery draining had happened several times previously.

There might be other 12 v drains happening, depending on which 'state' the Prius is in. All I know is that it is not in 'ready'.

This napping might be done better in 'ready'

 

A little recalculation.

First, the halogen headlamps will draw about 4.5 A each for a total of 9 A. I've measured them. Remember, if the car isn't in "Ready" then the 12V system voltage isn't 13.8, it's the battery voltage (probably around 11.5 to 12), so the lamps draw a little more than you would expect. HIDs draw approximately half that of halogens.
The stock 12V battery is around 30 to 35 A-hr, so a -fully charged- battery should last at least 3 hours. Even when half drained it should have no problem starting the car.

I would guess the battery may need replacing, or, perhaps the ground strap is corroded and the battery isn't being charged properly. This is common and confuses people all the time. I suspect 30% of battery replacements (not just Prius but all cars) are replacing "good" batteries and "fixing" poor connections to the battery in the process.

 

The 09 has an icon on the dash that tells you the lights are on. No idea if it's on previous models.

ETA: However if you use the fake-DRL feature, you get so used to this icon that it really just becomes a second READY light...

 

It isn't. For whatever reason, I didn't consider that.. duh.

ETA: Now I really feel dumb. I went out just to make sure... and it DOES stay on. However because the dash lights are dimmed (due to the lights being on), it was difficult to make out in the current lighting conditions.

 

Do note that there are two settings for the dash lights. The car will automatically select the setting you "program". Set them in the sun (daytime) and the car will remember that. Set them at night (dark) and the car will also remember that setting.

And just to "muddy the waters" a bit, Canadian cars have an automatic headlamp position on the headlamp switch. But the lights do stay on when you shut down and don't open the drives door. But not all the time. I still haven't figured out why they stay on sometimes and not others.

More mud. The DRLs will stay off when you start the car until you release the parking brake. But they won't go off when you reapply the parking brake!

I'm getting dizzy!