Hmmm - Yep Could be!
If R/R's gone then battery could well have been boiling the acid - which being dilute sulphuric acid would explain the eggy smell.
The noise could have been battery breather and / or acid spillage onto something rather warm.
If you have access to a voltmeter / multimeter, start bike, and put meter across battery terminals to see what voltage R/R is charging at.
If it's above 14V then the Regulator Rectifier is fecked, the battery is probably goosed also, especially if it has boiled, plates will be well warped.
Shouldn't cost anything like £168 to put right though
New battery - go for a German made one not cheaper Far East crap, they're false economy - IMO.
Don't bother with Storm R/R even the newer finned version will cost you too much dosh. Go to road rash or other bike breakers and get yourself an R6 or R1 R/R should be about £10-£15.
With 5 male & 5 female spade connectors and 5 short lengths of wire, you can patch between the Storm loom & the R1 R/R socket dead easy.
See this link for
R/R mod as above (the spades are just my spin cos I didn't want to chop loom).
If you have any probs, giz a shout I'll come give you a hand.
Graeme.