Funny smell - battery?

I've done a quick search and couldn't see anything, but i could be being blind.. and i hope this is the right place.

Riding along on the bandit and i noticed a rotton egg sort of smell, am i right in thinking this could suggest the batteries had it?

Bikes not really been used for a year, then my dads used it every day this week and i've started using it too while the sv is broken. But my father wouldn't notice if something was wrong, unless it fell apart under him (i.e wing mirror hitting him as it left the bike)

[Biker Biggles]

Thats the sort of smell batteries make when they are overcharging and "cooking"
The next step is for it to split and dump acid all over the bike.You need to get a multimeter and check the charging system as per several threads on here.This will tell you what is wrong and you can sort it from there.Dont just buy a new battery and hope for the best,as it will probably just cook that as well.

Thankyou

I'll get my father to find the multimeter and have a look for the threads.