I have just bought a new battery for my series I Aprilia. After research on the net and in my local LSUK, I found the best and cheapest option at
http://www.tayna.co.uk/W501BX-Exide-Equivalent-Numax-Car-Battery-P3986.html I ordered it on the net at the weekend and, for an extra £2.75 had it delivered at 09.00 on Tuesday. Total cost is £110 for which I got a classic hard black rubber 92 amp/hour battery. Everybody else was more expensive or of lesser capacity and it fits very neatly in the hole. Tanya have a range of classic batteries in 6 and 12 volt as well as everything else. Thoroughly recommended, no commercial link on my part just a very satisfied customer. The battery does the business too!