Convert your Prius to Plug-in

This guy can really help you: http://www.hybrid-synergy.eu/showthread.php?tid=56644

DIY Hybrid Check

You can use Torque Log Analyzer to check your HV Battery health.

This procedure has been used to diagnose batteries with error P0A80 or “Check Hybrid System”, by identifying the faulty block.

You'll need:

1. Android phone (a low-end model is fine, even without any SIM, a wi-fi connection is enough)
2. Torque Pro from Google Play (the free version can't be used for this test) https://play.google.com/store/apps/details?id=org.prowl.torque
3. Bluetooth OBD Adapter: http://torqueloganalyzer.blogspot.it/2015/02/obd-adapters-database.html
4. Custom PID list
   Yaris, Auris, Prius 3:
   https://drive.google.com/file/d/0B8xG59QDgvQ3MWRGaFJpNFV1dFk/edit?pli=1
   Prius 2:
   https://drive.google.com/file/d/0B8xG59QDgvQ3OEl1dnBqSkxNRTg/view?pli=1
   Just download the .csv file

Follow this steps:

1. Install Torque on the phone
2. Load the custom PID list by following this tutorial: http://torqueloganalyzer.blogspot.it/2014/01/loading-custom-pids-on-torque.html
3. Configure logging as shown here: http://pleasedonttouchthescreen.blogspot.it/2013/06/torque-logging-tutorial.html
   You may only log PIDs specified here: http://torqueloganalyzer.blogspot.it/2014/12/hv-battery-fitness.html
4. In order to collect significant data, we need to cause a battery discharge. We'll use the same method used by Toyota while performing the Hybrid Check:
1. Push the brake pedal with your left foot
2. Switch to gear R
3. While keeping the brake pedal pressed, push the accelerator pedal to engage the electric motor. The car won't move anyway, because of the brake pedal.
4. If the petrol engine kicks in, decrease pressure on the accelerator, to turn it off.
5. Keep going until battery level gauge is at 2 bars and the petrol engine starts to recharge it.
5. Collect log using the above steps.
6. Load log into Torque Log Analyzer, as exaplained here: http://torqueloganalyzer.blogspot.it/2014/08/tutorial.html
7. Select HV Battery Fitness in the Analytics section and run.

A fine battery will show uniform block behavior, as seen here:

While a faulty battery will have its blocks scattered:

Seasonal Fuel Economy Variance

Here is one year of gas consumption data from my daily commute trip.
Chart shows how winter affect consumption: fuel economy is better in warmer months; more than 1 l/100Km in my test case.
It's a 9+9Km trip to work and back: a longer trip will lead to better and more consistent fuel economy results.
Anyway, this is a real-world scenario: car was between 20.000 and 30.000 Km while these data was collected. I expect even better results when the car will have more kilometers under its wheels.
Time will tell.

Learning to Brake

Toyota Hybrids have 2 braking systems, both controlled by the brake pedal.

1. The first is the friction braking system, as in classic cars, which slows down the car by pushing the brake pads onto the brake disks of the wheels.
2. The second is the regenerative braking system, which uses the electric motor to slow down the car while charging the battery with the kinetic energy recovered.

The second one is the one you should use as much as possible to optimize your fuel consumption.
Given that both systems are controlled by the same pedal, it’s important to understand how to use it correctly.
As a general rule, slower, gentle pressing of the brake pedal will trigger regenerative braking, while sudden and stronger pressing will force the friction system to kick in.

Being primarly a foot sensitivity issue, some kind of feedback will help you to better judge your braking performance: this can be accomplished by using Torque on your phone.

You’ll need the Torque Pro Android app; the free version doesn’t allow customizations.

Import the custom PID csv file as explained here.
Go in the “Real Time Information” screen

Select “Add display” from the menu

Select the “Graph” display

Select “Wheel Cylinder Pressure Sensor”

Select a size according to your phone screen size
Long tap the newly added chart
Select “Display configuration”

The default scale won’t allow you to clearly read transitions, so set maximum value to 0.8 and minimum value to 0.1

Turn on your car and pair the bluetooth adapter.
Test it by pressing the brake pedal with the car parked.
You should see a spike in the chart.

The chart displays the last 9 seconds, so you can actually focus on driving and check the screen later, when safety conditions are met.
A good, fully regenerative braking will show a flat line

Please keep in mind that under 12 km/h, friction braking will always kick in, no matter how light you push the pedal.

Estimated Resistance

Block resistance values reported by OBD are suspected to be inconclusive, or at least they show a strange behavior:

User Lesolee from the Toyota Owners Club forum, suggested to apply Ohm's law to calculate resistance of each block based on measured voltage and current.
So, for each measure of every block, current and previous voltage values are used to calculate a delta V, which is divide by delta I, obtained from current and previous battery current value.