zip battery queries.

i wanted to know if the lumie zip would run through the mains.ive already read a response to a similair question.but it wasnt very thorough.when the battery eventually no longer holds a charge and is therefore useless,will the mains bypass the battery and continue to operate the unit.i dont fancy forking out for new batterys evrey time one has seen the end of its life.if this is the case,will you supply a new battery service and roughley how much will this cost.im sure this is a question all consumers will need an answer too.as this product could work out very costley.thank you.