i know someone who put some different/better battery kit into his prius and he has nothing to complain about. he gets around 150 miles per gallon. only has to go to the gas station a few times per year. charges his batteries with solar panels. and since the gas engine is only used half the time, it doubles the life of the engine to around 500,000 miles. he is saving loads. toyota of course found out about this and started making prius' (pre-ay..) so that modding can't be done. the lithium batteries manufactured have changed in the last few years to be made to not be utilized in any which way.