Having read through the many useful comments about battery shelf life, in particular Li Ion batteries, I am concerned that any savings both financial and environmental will be blown away by having to spend 200 odd quid every 6-8 months on a replacement. I live in Bath where there are many steep hills, and although my daily commute is only about 5-6 miles in total, it will require a great deal of power getting from A-B. Is it really that difficult to get ones hand on Ni batteries or is there any other way to reduce this potentially enormous annual cost ( I understand that Li Ion batteries should not be fully discharged etc) .. I fear another First bus season ticket coming on!!