They are extremely bad for the environment! Every Li Ion or Li-poly batteries (Ni Mh as well) are made with huge toxic waste and pollution. Just the Li mining process involves several steps of acid extractions which waste goes where?? Some of these step are allowed only in china on an industrial scale.
Please, DO NOT by any hybrid vehicle if you care for your environment!!
CO2 is not nearly as disastrous than the toxic waste associated with battery making!