Batteries Question

Unless your Prius is in the "Ready Mode" all of the power comes from the 12V battery, which is only about 1/2 the size of the 12V battery in most cars. So if the car is "Off" or in the "Accessory Mode" or the "On Mode" all the power comes from the moderately sized 12V battery. When you put the car to "Ready" the hybrid battery charges the 12V battery if needed and the engine will run to keep the hybrid battery charged when needed.

The hybrid battery starts the engine but it can't do the job unless the 12V battery still has some charge in it because the 12V battery is needed to close the relay that connects the hybrid battery to the car. If your 12V battery is dead you can jump the car with a connector under the hood, read the owners manual first though, if it's done wrong it could be expensive.

 

Just talked to a technician. 12volt batteries have a 3-4 year life.
Hybrid battery supports 12volt system to a point.
Hybrid battery has to preserve itself.
Technician told me if that big battery was run down it is a big problem. They have to have a regional service department come in to fix the problem.
He said the a/c runs off of the big battery and that the starter runs off the big battery. There is a step down inverter to the 12 volt system from the big battery.
Said that it is recommended if the car sits for 14 days or more that the 12 volt battery be disconnected.
If sitting in the car running the a/c, radio, etc. with the ready light on(IGN-ON) then a demand for the gasoline engine should occur to recharge batteries. Which makes sense since the big battery supplies a step down inverter to the 12volt system.
Might be a good idea for people to practice getting in the car without the 12 volt battery connected. Know how to access the 12 volt battery. Know how to access the jump terminal in the fuse box under the hood(easier than getting to the 12 volt battery when dead).
Carry a portable jump start battery and/or jumper cables just in case. Especially if your 12volt battery is 3 years old or the car is going to sit for 14 days or more.

 

Prius2007:

You are overthinking this.

In traffic, the ICE will turn on whenever the Traction battery needs charging. This generally occurs when there are one or two bars left on the SOC.

The 12 v battery, in turn, is charged by the traction battery when the car is READY.

Also, the SOC meter only shows the charge states between 40 to 80%. So even with just 1 bar left, you have at least 40% charge remaining in the Traction battery.


Best wishes,

Frank

 

Last night, I left a restaurant and was cruising at 38 mph, no wind, 68 F, relatively flat, headed home and noticed:

• initial traction battery operation down to and including two bars - I had expected the ICE to start earlier.
• ICE ran for a while to bring four bars on traction battery
• steady state, ICE on/off to sustain four bars at 38 mph, the expected operation

I suspect we could make a chart of stable traction battery bars as a function of speed AFTER taking out what may be an initial traction battery drain and recharge. Anyone else notice a traction battery dip before the SOC reaches a steady state?

Thanks,
Bob Wilson

 

I'm sure I've read somewhere that you can force start the car with a flat 12v battery by holding down the power button for 30 seconds.

Is this correct or have I just dreamt it?

 

You didn't dream it, I think that's refered to as the "emergency start function" in the owner's manual. I don't know if it would overcome a low 12V battery or not, if the 12V battery is completely dead I think it would not. My understanding is that the 12V battery is required to power up some circuitry before the traction battery can come on line. If my car won't start some day I'll sure try it though.

Another emergency start procedure mentioned can be used if you have a dead key fob battery. Hold the key fob right next to the power button when you push the button and it is suppose to sense the fob even with a dead fob battery. I haven't tried that either.

 

Has anybody tried the above and had experience of this?