This is the simpleest way to get harmles high volteges of an batery!
The transformer can be any mains transfomer(110-220V to 1-24V)
Whith the right transfomer it is posible to generate up to 2000V!!! (Don't wory its not dengerus becose of to low curents!)
these transformers normaly have 20-40:1 ratio so how can it make 2000V(200:1 ratio reqierd)?
Its becose some transformers have an good magnetic field breakdown efect(energy is storen in an magnetic field an then relesed as an high...