SoC drains to two bars every other night

You and the OP could both take 2009Prius's advice.

When the car is first started, depending upon the circumstances, there can be a high initial demand on the HV battery and the charge can drop relatively rapidly.

Some things that can exacerbate this are

- A lot of A/C required. When the car is heat soaked the A/C has to work very hard to initially cool the car. All it's power is drawn from the HV battery. If you can have the AC off and use the windows down to get the heat out for the first few minutes of driving before switching to AC (and putting the windows up) then that can really help.

- Poor condition 12V battery. This will lose charge rapidly, especially in the heat. When you start up with a low 12V battery the DC-DC converter works hard to recharge it rapidly and draws it's current from the HV battery.

- Even when the temperature is warm the cat's will still be too cool for the engine management system to fully use the engine power for the first 30 to 40 seconds. So the car will preferentially run on electric power for a short while.

So you see everything can be hitting the HV battery hard for the first few minutes after start up. If you let the engine idle in park for 30 to 40 seconds before driving it makes quite a big difference to how well the HV battery copes here.

 

Check the easy stuffs (12V lead acid battery, etc..) as others suggested. If you believe the issue lies in the HV battery, you can do the following.

You can get a $49.95 OBDLink SX OBDII USB adapter and use PriiDash software to pull data of your HV battery modules. There are 14 modules and by looking at the voltage and internal resistance, we can compare the health of each modules. I am sure 2009Prius can help you out with the graphs. He has done it to compare mine (2006 with 150k miles) and his (2009 with 20k miles). I'll be interesting to see how they compare to yours.

Alternatively, you can get $85.81 Kiwi bluetooth OBDII adapter from Amazon plus $5 Torque app from Android marketplace and pull the same data. You can even view LIVE data from an Android phone.

You can mark down the State Of Charge (SOC) of the battery pack right before you shutdown and compare the SOC upon the next day start up. If the difference is too great, the HV battery is draining overnight.

 

OK,

Forgive me if this question seems insulting, but sometimes it helps to address the most basic questions, so that we are sure are assumptions are correct.

When you exit your car after driving, you do "power off" the car, correct? If you left the car in a "ready" state, it would slowly drain the traction battery over time and the engine would run to charge it. I'm guessing you do shut it down, but on the off chance you aren't, this would be a simple way to address your problem.

 

It sounds like he shuts it down because when he started up, he sees (6?) blue bars and suddenly it became (2) pink bars. That's how I interpreted it.

 

The engine has to work harder if the battery is not assisting or unable to. If there is a weak cell in a module, it can do that. My guess is, the car may not throw an error code if the threshold is not reached yet.

The only way to tell is to use a OBDII scan tool. Dealer has that tool but they may not tell you the results but you can ask for it.

 

You plug OBDII side to the OBDII port under the steering wheel and the USB side to the computer.

 

Ok! So with a OBDII tool, you can capture the battery State Of Charge before you turn off the car and compare it when you turn it on the next day. You'll be armed with the percentage of loss over the number of hours.

Not all the OBDII readers can show the hybrid battery SOC. The ones I suggested are the cheapest if you already have a laptop or an Android phone. If you have neither, get a ScanGauge II which comes with a screen.

 

Florida is a CARB emission state so the hybrid battery has 10 years / 150k miles warranty. The catch is, that started in 2006, so prior year models may only have 8 years / 100k miles coverage. Check your owner's manual and it should be in there. If you are covered under warranty, we'll worry about getting Toyota replace it for free. They wouldn't want to replace it without an error.

In order to do that, you'll need to have hard numbers to present and OBDII tools can provide that.

I think getting OBDLink SX is the cheapest option but it is a bit tricky to set it up. Torque app and Kiwi is easier but you need an Android phone. If you don't have one, you can get a used one for $50-$70. SGII is easiest to setup but it can only pull the HV battery SOC. It cannot pull individual module voltage and resistance.

 

See this thread to get you through with the setup. Once it is up and running, it'll automatically log the HV battery information in your F: drive.