You can start the Prius hybrid system with a half dozen D-cell batteries. No kidding. I live in a area where a battery is expected to die in 3-4 years. Its not from the cold. I have to say here that you have exceeded your level of actual knowledge. Heat kills batteries faster than cold does.
How does one exceed one's level of knowledge exactly? It's not the cold directly, it's the strain it puts on the battery.
In 'normal' cars the cold makes the engine oil thick, the transmission lube thick, the diff lube thick, etc. None of this matters in a Prius, as the 12 volt battery does not start the engine.
While I've not experienced any lengthy shutdown time with my current Prius v Three (Three not III because uppercase Roman numerals were used for model designation year 2010 only) did have occasion with old Gen 2, 2004. In that case was on an extended 28 day trip with car parked at airport (it was also August timeframe). When got back the car started right up and never noticed any problems. This occurred when the Gen 2 was six years old. Don't know if this helps but is from practical experience.
My previous car used several electric fans in place of the belt driven one. I was happy with the deep cycle battery that last over 6 years while the regular one was about 4 in PA. After reading this thread, I checked *bay price for both and guess what: the deep cycle = $147 and the OEM = $170. (price as of today). In this case, I'd rather go with the yellow top deep cycle.
I think it matters where the voltage readings are taken (engine fuse box vs. battery terminals). There is a difference of about 0.10 - 0.15 v from measuring directly at the battery or the terminals in the engine compartment. That's why I mentioned where the readings were taken. You mentioned ideal voltage with "no load". Unless you disconnect the 12v battery to check the voltage, there will always be parasite loads on it. "Dangerously" is a bit of an exaggeration in this case since we are not using it to crank the engine. Unless you sit in accessory mode for extended periods, the 12v battery doesn't do a lot of work. Most of the time, it is being charged (maintained) when the majority of the cabin 12v items are drawing from it. Regardless, I don't think the computer would fail to power up at 12.1.
There should be no difference in voltage if there is truly no load. The difference is a tell-tale sign of a load somewhere.
Believe it or not - there HAVE been numb skulls that leave ignition on with ICE not running (warmed to stage 4) - car in neutral - walk away, and end up with dead traction packs. The aux battery? cheap in comparison. .
I've carped about this bitterly in previous threads, but that should never happen. Not that I'd ever want to test it, but there should be some sort of protection that cuts off all battery drain long before the battery is in danger of going dead.
Of course, it is part of the car's complex electrical system. To quote myself: "Unless you disconnect the 12v battery to check the voltage, there will always be parasite loads on it."
Honda Hybrid outsold the Prius in several Asian country because the Prius can not set to"N", while parking! This is the requirement when you park your car at most shopping malls so that you can park perpendicular in front of the parked cars and when they want to come out, they or the passerby or the security will push your car out of the way. This is the normal practice over there.
OK let's guess at what he was really trying to say. Can you shut off a Prius while the selector is in N......and have it actually shut off........and NOT have the transmission automatically lock ?? As for uneven terrain, you just apply the parking brake........like you SHOULD be doing all the time anyway. If the parking brake is electric and can't be released without the key, that could be a problem too.
I meant to say parked and left the car unattended then go shopping or whatever. They locked the doors and keep the wheels straight with gear in "N" for the reason mentioned.
