Accessories running down battery when car stopped

You need to fully charge the 12v battery and test it (with a car battery charger for about 10 hours). If it fails a load test, you'll need to buy a new one.

You also should not run anything on accessory mode for more than 15 minutes, the little Prius battery will drain easily and leave you stranded again.

 

12v car batteries are not expected to last 10 years, even in a Prius. If you are using the original, change it now.

 

After the jump, you drove 20 km and then left the car in P with the car still in ready mode...and it wouldn't start (next time?) A healthy battery takes little juice to boot the car and that cycle given after should have been more than enough. Check you cables for corrosion, but sounds like you just need a new 12 VDC battery.

 

If you are using electricity, be in Ready. Try to never use electricity when not in Ready.

Rats, I had good advice on where to buy the cheapest and best battery, but you live in NZ, not US.

This may be close:
Repco Car Battery 430 CCA - NS60LX MF - Repco | Repco New Zealand

 

Do note that the Prius' 12V charging system is surprisingly slow. It takes many operating hours to bring a flat 12V battery up to a reasonable charge. 20km is only 10-20 minutes, so your 12V battery was still almost flat. An overnight charge from a plug-in charger or battery tender would do far better.

Though this doesn't explain why a car left in "READY" mode, quit running.

 

You figured correctly. As already mentioned, keep it in READY mode to run accessories. The battery is sized to boot the computers and close some relays, not to run fans and stereos.

This is exactly how it should work. The indicator on your dash, if you weren't already aware, is for the traction battery, not the 12V battery.

Yeah, a short drive is not enough to recharge a dead 12V in pretty much any car. If it would need several hours connected to a dedicated battery charger, there's no reason to expect it to be faster with the car's charging system.

 

I run a fan I put on my dogs crate in the back. I changed the 12v supply in the center console to
supply power all the time. I run it about 30 minutes, off for 30 minutes, then run it for about 45 minutes.
My Prius starts each time. The battery is almost 2 years old.

 

You probably need to charge it from time to time since you don't drive for long periods.
I drive 2-3 hours at a time 4-6 times a week, so it get a good charge.

No sport, ASR, American Street Ring.

 

Keeping it in READY will let it run the fans till you run out of gas in a few weeks, assuming a full tank. As long as it's in READY, the DC/DC converter will feed power from the traction battery to the 12V battery to maintain that level. Makes no difference if the engine is running -- just so it's in READY mode. The engine will run whenever it needs to add charge to the traction battery. People camp overnight in the Prius all the time this way.

 

What about running a fan off of one of those USB power banks -- the kind mostly used for charging cell phones? The power bank only charges when the car is on (READY or ACC). When the car is off the fan can only ever deplete the power bank and not the 12V battery.

 

Or a UPS backup battery. They are about $15-20 depending on size you get.
Then you can have it hooked up the the accessory plug that will charge up that battery only when
the car is on.

Update: I found this link: Mighty Max 12v 7000 mAh Compatible Battery for UPS APC Back-UPS BX1000 - 2 Pack 730052395754 | eBay

 

Ooooh. Don't mislead like that. The car only charges the battery in READY mode. That's the only mode where it charges the battery. Check the manual if you're not sure.

 

Rats. Too late to edit my previous comment. I should have added:
But don't feel too bad. I've made similar mistakes as have most of us. It's just that that mistake can leave you stranded. Hence my alarmed reaction.

 

How will you control the current going from car to battery? These apc battery will blow up if the recharging current is beyond spec charge amperes. I replace these in the it field on a regular basis, I wouldn’t throw a 12v source to it without amperage control.

 

On acc, power still sends to power bank if connected to 12v cigaret plug. But if you leave it plugged in with car off, you run into the issue of car keep unlocking when you try to lock the car

 

Considering that the person will have the fan blowing for a while, the battery will be low.
He stated he doesn't drive that much so it's doubtful that battery would get fully charged at
1-2 amps.
It was just an option, to consider.

Results may vary.

 

Uh Jer, this is the kind of power bank I'm talking about. You charge it when you're driving or when parked in ACC mode, then use it when the car is OFF. You'd have to reallllly work at it to strand yourself this way. (Fun fact: In Gen 3 lift-back ACC mode turns off after 1 hour. In PiP it's only 15min.)