Today, I got my prii tinted. The guys left my car in the on position to adjust the window while they applied the films. About 20 minutes in, the windows stop working. They then jumped the car and started the car instead of leaving the car in the on position. My question is, when the car is left in the on position for a long time ~15-20 minutes is there a safety shutoff for that? Or do the 12v really die only 20 minutes without the engine on? I do have navigation. When they were complete, the traction battery was at 2 bars. When I went in, it was full. Does it look like I'll need to replace the 12v? I also have a "brand new" 12v from last year sitting in garage. Will that hold charge? Thanks
For long periods of 12V use, put the car in "Ready" mode. This will keep the batteries charged, and the engine will run only when needed. The 12V battery in the Prius is fragile and will not take very many deep discharge cycles. Yes, it can die in 20 minutes. It may be OK. It depends on how old it is. 12V batteries do not like to sit unused, as they will self discharge and sulfation will set in. Put the unused battery on a battery charger/maintainer. The best thing is to use it. If you experience problems, you will want to test the 12V battery in the car to see if it is still strong.
The power drain when the car is left IG-ON is quite high, as you learned. It is likely that your 12V battery was marginal since it only lasted 20 minutes. There is no "safety shutoff" other than your battery dying. If the "brand new" battery was not periodically charged over the last year, it may have diminished capacity now. I suggest you fully-charge the battery overnight, then install it and see what happens. A fully-charged AGM battery out of the box should read 12.9V, after allowing surface charge to dissipate. The Scan Gauge reading should be reasonably accurate but if you have any concern about that, use a digital multimeter to confirm the voltage reading.
Nh70 has summed your problem and solution up well. The only observation I will add is that the car must not!!! be in neutral, as in neutral the engine cannot start to recharge the HV battery and then in turn that cannot through the DC to DC converter charge the 12v battery once the HV battery is discharged. The system will work in any other position "but obviously for safety park should be used" but as I said NOT neutral. John (Bitprius)
So I haven't driven the car since yesterday. This afternoon, I plugged in my scangauge2 and it read 9.6 completely off. When I pressed power button once, it was like 11.9 then 14.1 when cars started. I think I need to replace it. I'm charging it with my 1.5amp slow charger as we speak to get some life back. Think it'll last or is it done?
I just replaced mine recently, it was in the 9 volt range after sitting overnight which is completely dead for a 12 volt lead-acid battery. It is most likely that the one in your garage is dead, too. Flooded lead-acid batteries need to be recharged every month in warm weather, AGMs like the Prius 12 volt battery can go a bit longer, but not over a year. Came out this morning and one of my kids left the rear seat light on all night, I was very happy to have the replacement Optima in there. Started right up.
