| Frank, as you know I have the same battery fitted to my bike. In the last year it has had two serious overloads, first when the starter solenoid shorted against the cylinders head and virtually flattened the battery and then a few months later the voltage regulator shorted internally and damn near went on fire. Fortunately the battery re-charged with no problems on each occasion although I think the first incident may have hastened the second.
As has been suggested, overcharging is a likely reason for the battery bulging like that.
Check the voltage across the battery when the bike is running, It should be about 14.3V at 3,500 rpm. No more than 14.5V at most. | 
Hybrid Mode
