Coopns, you won't get an electric shock from 12V, even if you grab one post with one hand and the other post with the other hand. The dangerous part is electric sparks. If there's any hydrogen buildup, which can happen around batteries, and you introduce a spark, you can have an explosion, although this is a rare occurence. Good ventilation and eye protection would be very well advised while doing the job. I don't know if I'd go to the extent of donning rain gear, but if you want to be extra careful, go ahead. I've done several of my own battery changes, even with leaking batteries, and haven't had a problem. Expect to see a spark when making the final contact, though. That's normal and won't hurt you.