Ive been running 1 now for about 18 months and it stood from September last year till earlier this month in a cold damp unheated garage. Tested it with a volt meter before re fitting it expecting it to have dropped voltage slightly but it was still showing a healthy 12.3V. (and when refitted cranked the bike over with zero problems).
The only negative with Lithiums is that they may need balancing, but this only really becomes a problem if your running a total loss system (the bike does not recharge the battery whilst running, such as a race bike).
Had mine from this guy here -
http://www.ebay.co.uk/itm/LIGHT-WEIGHT- ... 5d32d3fd75Really helpful and answered all questions i could throw at him