What part? The battery! I mean it is the original on a bike first registered in May 1997 so it hasn't even made 14 years old yet! What is the world coming to if a battery won't last, well, at least sixteen years ha ha. Shocking quality and worthy of a 'disgusted of Tunbridge Wells' type Radio 4 comment!

By the way, I think if you replace your battery then a genuine Yuasa YTX 12-BS is the best bet.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... K:MEWAX:IT