Battery terminal bolts dissovling.

Rider mower, 12v battery.

I have had to replace the bolts many times. These are the latest. The negative terminal bolt is fine, the positive terminal bolt is dissolving away where it is exposed to air. I tried using stainless steel bolts last time but they don't last either. I think I used some of that battery post grease they sell at the auto stores. Yesterday when the mower would not start, I took the cover off and found the positive post covered under a mount of red foamy goop. What's going on? I think I tried brass bolts & nuts before with similar results. Would copper bolts help? I've had to replace the positive battery cable before but it does last much longer than the bolts. The terminals are normal lead covered, the cable end is a regular electrical terminal. Is this from overcharging? What should the voltage be? I think it is very strange that the parts of the nuts & bolts exposed to the air are the parts that are dissolving. You can see the "before & after" effects. (negative bolt & positive bolt).

IMG_1375 by rickpaulos, on Flickr

IMG_1376 by rickpaulos, on Flickr