as walkura pointed-out before, ALWAYS USE SAFETY GLASSES, gloves, and if is possible a mask to cover your face. do this job in a well ventilated area, outside, or if cannot, install a small fan towards the battery to remove the hidrogen which may accumulate and cause violent explosions. i have a friend which carries some scarface from an attempt to repair a truck battery, the H ignite from a spark and one battery compartment blew up completely, splashig acid everywhere.