Has anyone gone down the lithium battery route ?
If so which make?
They are a fraction of the weight, perform better and have extended life compared to lead acid equivalents.
The Caterham guys use the Powerlite PS-20 which will fit the original battery tray and has over 400 C/A.
Wonder where you read about the extended life compared to lead/acid.
Tesla I believe guarantee 80% capacity after 8 years. They are able to offer this because they double the 100% capacity ex factory and initially charge to 80% of this and discharge to 30% gradually scaling the range up until using 100% of remaining capacity. Clever eh! 
Indeed, Tesla never actually state the absolute capacity of the battery in Kwh. They talk about available capacity which is not overly helpful as no one charges to 100% and runs to zero.. zero isn't really zero, there are a few % left. There is no doubt that Tesla batters have undisclosed capacity which the battery management software can make available. I don't believe that the batters have double the nominal capacity as there are not enough cells in the battery packs, but they certainly have some spare. Tesla battery management software is at the heart of their remarkable battery performance, both charging and discharging. The packs work at a nominal 400v, but mostly between 300v and 350v.
The battery in my Tesla M3, made in China, is a nominal 75kwh, with it is believed 72kwh available. I don't let it discharge below 5% and normally not below 10% and I normally charge to 85% on a 240v 32A A/C charger. But it can be charged at a Tesla Supercharger at 400v, 250kw DC. On such a charger, arriving with 6% it charges at 350kwh and claims to be adding 1000 miles range an hour. The charge rate slows and at 85% it is charging at about 75kwh. To get from 6% to 85% takes 40 mins and leaves me with a range of about 300 miles.
Using Superchargers does shorten battery life, but by how much is unclear. If you set the navigation software to take you to a supercharger the car pre-conditions the battery so it can be charged at a high rate: in winter it uses battery capacity to heat the battery.
As far as Li batteries in ICE cars are concerned, I'm not convinced that charging them from an alternator would be optimal, some form of software interface would be essential.
