Mitsubishi i-MiEV lack of range

i have had my car for 13 months and experiencing reduced range. the first 8 months i was getting 72-78 mile ranges driving in eco mode 90% drive mode 10%. my trips never change commuting within 8 miles of home 50/50 highway/ city. i started noticing range going down to 65-69 back in oct. and the past two months the range has been 60-63 in the cold months of jan and feb here in PA my driving habits and driving trips never vary , top speed traveled 55mph. i park in a garage and charge on a 120v household outlet. my thoughts are the battery is degrading something i have read about in the manual. i never recharge unless the battery is down to 4 bars or less. i also noticed when i recharged outside at a public station with outside temp. at 20 degrees the battery charge even tho i had 16 bars was not full because my range showed 54 has any one experienced these problems?
Comments
Sounds to me like the typical behavior of an electric vehicle in colder weather. I don't think battery degradation is the problem--I think the basic laws of physics are the problem.
You might find this article interesting:
http://www.greencarreports.com/news/1081982_electric-cars-in-winter-six-steps-to-maximize-driving-range
second thought on reduced range I recently got a software update letter recommended by the manufacture it was a recall letter for a vaccuum pump also The manufacture's letter stated it was necessary to update software for compatibility issues with the charger After getting the update done at the dealer in jan i noticed a drop in range and the mileage i can travel per bar is 3-4 miles instead of previous 4.5-5.5 miles. has anyone else received the same updates and noticed any difference? i know the leaf and the volt have software that control the maximum charge capacity of battery to prolong battery life so at a full charge it is not actually 100%. I have not read anything on the imev where this is done. may this update limit capacity??
followup to the upgraded software : the range gauge was affected by the software my range started going up after a full drain of battery and recharge my battery was as low as 2 bars and then i recharged it till the battery orange charge light went out the range reset to 77 miles i guess software changes done at the dealer did not apply to car computer untill the battery was drained low this i hope is helpful to others