CNG Conversion for Prius

I did the conversion to CNG too, as CleonII did. Actually we let install the CNG by the same garage.
As Cleon II says, the car runs perfectly and -given the CNG prices here in Italy- you can do about 100mi with 4£.
The only minor drawback is that the battery "lost" a row. This probably because of the slight ICE power loss caused by the CNG. Thanks to the ecvt the performances are almost the same as with gasoline, you can't feel you are driving with CNG, only on steep inclines you can feel the reduced power. On flat roads I observed that at same speed the ICE turns about 200rpm higher when running on cng.
Transition between the two fuels are not noticeable. If the coolant temperature is below 86F the car starts on gasoline and switch to CNG as the temperature rises over 86F, otherways she always starts on cng.
Thanks to the low fuel consuption is not necessry to install big cylinders in the trunk: we have two small cylinders (17 liters each) in the spare tire hollow and two bigger cylinder (24 liters each) under the trunk cover, this is sufficient for about 200mi and the the trunk remains fully available. Nonetheless the cylinders weigh 70kg, so we let install reinforced spring at the rear suspensions to recover the correct height of the back.

 

A small update.
After 15000km on cng I confirm that the car runs perfectly.
No lights on dashboard, no signs of valve wear (touch wood...), no problems at all.
Mileage is about 27km/kg (8.1mi/lb cng) on highway, up to 35km/kg (10.5mi/lb cng) on normal roads.
Given the fuel prices here in Italy I saved until now approx 750€
Now I'm planning to install an ignition-ecu to advance the ignition timing at low rev.