Good advice above, but let me add one thing. Anytime somebody changes a battery (or does any work around batteries), they should wear safety glasses with side shields. When I was a youngster and just learning how to drive, I tried to jump start a battery. I got the cables crossed and the battery blew up. I was sprayed in the face with battery acid and received some minor acid burns. Fortunately, I had on glasses which saved my eyes. I'm sure battery acid in the eyes could be very painful and do quite a bit of damage.
Jim