s40 battery replacement
 

I bought my first bike, a 2012 s40, on Friday, it seemed to be running fine. Guy I bought it from said he'd had no issues with it. Today it wouldn't start. Checked the battery, and its dead. It looks like there's some corrosive damage to the casing around the battery, I've attached some pics.
Only battery I could find in store was non-activated so I have to put in the battery acid and charge it myself which I've never done and don't have a charger for.
1. Is this corrosion an issue? How do I clean it?
2. Are there batteries for the s40 that come activated and charged?
https://cimg0.ibsrv.net/gimg/suzukif...b8107acc3e.jpg

Thanks in advance for the help!