TRUE / FALSE (and please discuss). 1. The 12v battery does nothing other than wake up the computer and provide power if in ACC mode. 2. Once the car starts, the traction battery provides for all loads. The 12v battery is just another load on the traction battery (because it recharges the 12v battery) 3. If you had a completely dead battery in a Prius that was incapable of taking a charge, you would never be stranded as long as you had a jumper box with a good charge. 4. Once started, the 12v battery could even be removed because it does nothing (just talking theory, not suggesting that's a good idea). 5. The Prius doesn't even need a 12v battery to be present, you could just attach a jump box each time to wake up the computer and start the car (again, just talking theory). I'm pinning down my understanding of the 12v battery function.
1 and 2 are correct... But 3 is not correct because a dead battery in a circuit is going to suck the life out of the 12v charge in the system. And if the dead battery can't take a charge you'll likely have the same problem if you removed the battery entirely after the car is in ready mode which is warning lights, error codes and system shutdown because the car isn't detecting the 12v that it depends on for all circuits to be running properly even though it's not actively drawing power but charging that circuit...
1. The 12-volt battery provides power for all of the loads (ECU memories, smart key operations, lights, horn, etc) that are enabled all the time. In addition, it supplies the infotainment system and 12v power outlets and a few other things, when in ACC mode. In addition, it supplies all of the car's 12-volt loads, including windows, climate blower, defoggers, electric seats, wipers, brake pressure pump, coolant pumps, etc., when in IG ON mode. It also supplies all those loads in READY mode for a second or two until the system main relays close and the DC/DC converter takes over the loads. 2. Once the car is in READY, the DC/DC converter output is in parallel with the 12-volt battery. Because the DC/DC converter output voltage is generally a bit higher, it is generally what's carrying those loads when it is active, and the 12-volt battery is getting a charge. The DC/DC converter is taking its power from the high-voltage system, not just from the high-voltage battery. When the engine is supplying charging power, or when you are coasting or regen braking, those sources of power are supplying the DC/DC converter and therefore the 12-volt system. At other times, the power is coming from the traction battery. 3. Depends on the capacity of the jumper box. An extremely-discharged Prius 12-volt battery can suck all the charge out of a smaller jumper box, even if the box was charged to 100% to start with, in less time than you need to connect the jumper box and reach around inside the cabin to try starting the car. 4. Yes, that works; that is my usual way of getting around #3. I get the 12-volt battery out of the circuit first, use the jumper box to make the car READY, then put the 12-volt battery back into the circuit so the car can charge it. Having the battery out of the circuit then doesn't harm the car. A gen 2 Prius may log a trouble code because the remote-sensed 12-volt battery voltage doesn't reflect what the DC/DC converter is putting out. In other (especially older) cars, don't do that. Conventional alternator/regulator systems depend on the battery being in the circuit. 5. You might be able to drive a Prius this way for a while before going stark staring bonkers. All of the ECU memories would be lost every time, all the recalibrate-after-battery-replacement things would always need to be done, and so on.
I'm suprised the computers don't throw up warning lights when you don't have a 12v connected? Wouldn't the computers notice that the 14v charge to 12v wasn't being received? As in when you have a discharged battery that's able to get into ready mode from a jump start it still creates all kinds of glitches in the system when driving it before its fully recharged, right?
Gen 1 and gen 2 have two wires that connect at the 12-volt battery positive post. The fat one is the main power cable and the skinny one is the DC/DC converter's voltage sensor, so it can react to the exact voltage at the battery, unaffected by any voltage drop in the wiring. The cars don't really panic if that wire's not connected. Gen 1 just silently goes to a nice default DC/DC output voltage, and gen 2 does that and sets a trouble code and a warning light. You can "take the battery out of the circuit" in more than one way, say by undoing the clamp from the battery post, or just unplugging the fat wire from the clamp. If you undo a battery clamp, then the sense wire and main cable are still connected at the clamp, and the DC/DC converter sees its own output voltage coming back, which won't seem weird. If you unplug the fat wire, the sense voltage stays reading the battery voltage no matter what the DC/DC converter puts out, which may seem weird enough to set a code. So you get a code and light telling you you did something weird. You already knew that. In gen 3 they still have the "remote sense" wire but just bolt it down in the fusebox. It allows the DC/DC converter to accurately sense voltage unaffected by any voltage drop in the, like, nine inches of fat wire from the converter to the fusebox. So taking the battery out of the circuit doesn't really change what the converter senses. Gen 4 had the switch to the more sophisticated Battery State Sensor and I don't know how that responds to your unexpected shenanigans.
You are still using a 12v battery to ready the car. Without 12volts, the hybrid system won't be "readied". If you didn't need the 12v battery, Prius wouldn't have one. Even the Tesla uses a 12v battery.
