I um have strayed from the fold a bit; purchased a bike that needs a new lithium battery. While doing near endless "lithium battery" searches to find a very elusive battery; size, power, features combo. I found this thread the definitive thread on Lithium Batteries in the Aprilia forum. If you are considering lithium it's near mandatory reading. Note the time span, this thread has been going for 8 years so far. It covers the early pitfalls and resulting improvements as they occur. My post "if approved" found near the end of the 7 page! thread hints at my latest "insanity" Don't worry it's just an aberration, if survived I have endless XS650 projects awaiting. Also my quick and not tested take is that the earthX batteries offer the best combo of features, power, and size if you are interested in a lithium for your custom XS, especially one with electric start. They aren't the cheapest, but cheap can really bite you in lithium tech.