I have got a Magneti Marelli 53034 Lithium Ion battery. It has worked very well, lots of cranking power, very light, compact and no need to keep it on a conditioner.

It was on this link: http://www.ebay.co.uk/itm/BATTERY-LITHIU...E-/191469157564

It seems not to be available there any more but may be somewhere else. Downside is the cost, about £165 a few months ago. There are probably cheaper Lithium Ion alternatives about now.