So assuming £16K base model for someone wanting to commute up to 50 miles a day:
6 months petrol approx 6000 miles x £price of petrol at today's £1.20 = £720
6 months battery = £30 ?
12 months petrol approx 12,000 miles = £1440
12 months battery = £60
18 months petrol approx 18,000 miles = £2,160
18 months battery range drops below 50 miles, needs a charge at work = £120
and so on to year three when the total petrol cost approx £4,500
Battery range has dropped to 20 miles so won't get to work and needs a replacement at £4K replacement.
So over 3 years in terms of fuel used it will just be more economical and assuming petrol shoots up, then even more economical.
BUT what does the owner do at year 3, renew battery or attempt to sell at massive depreciation because it needs a new battery.
Answer: wait until 2016, buy a 3 year old bargain and enjoy extremely cheap motoring for up to 50 mile range.
What battery warranty will be provided with these cars?