Making a plug in hybrid from series Toyota Prius

We have bought a crashed Toyota Prius in 2005 and by repairing it we have learned a lot about electric propulsion. After some time we found out that the car could be much better by having a bigger EV range and more energy stored. We made and installed additional 55V 53Ah Kokam battery where the spare wheel used to be. This battery charges the original battery and keeps it full for about half an hour and during that time, the consumption drops to 2,5 l /100 km because it runs with more electric support (green battery on dashboard). In summer when heating is not switched on it can also make some km of pure electric drive, but due to Toyota speed and accelleration limit for EV mode it is quite useless or usefull just on parking lots and 30 kmh zones. The cost of such conversion is not really low (3500 €) and that is probably the reason why Toyota has not done it yet. But it works fine and especially on short trips it saves a lot of fuel.

Crashed Prius as we bought

Additional 12V PV cells to keep the small 12V battery always full

Converting our Prius with the help of two American friends