'13 series configuration Meanwell HLG-320H, 30 amp quick charger fuse
'14-15 Green Watt Power EVC-116-1200 charger, 100 amp quick charger fuse (S/SR/DS)
'13 nissin front/rear brakes; 43 mm fast-ace forks
'14 nissin front, j juan rear brakes; 43 mm fast-ace forks, increased front/rear travel (S)
'15 bosch abs, j juan front/rear brakes; 41 mm showa forks/rear suspension
'13 25 Ah Farasis cells, 2 year battery warranty
'14 25 Ah Farasis cells, 5 year battery warranty
'15 27 Ah Farasis cells, 5 year battery warranty
'13-14 angular mirror style (used since 2011)
'15 rounded mirror style
'13-14 IRC tires
'15 pirelli tires
'14-15 have a 25 Ah power tank option to extend range by 20-25%
'13 koso gauge
'14-15 custom gauge
'13 has '12-style side plastics
'14-15 have plastic side fins that direct some air to the motor
'14-15 FX has twin projector headlights, passenger seat and pegs
'14-15 SR (not available in 2013)
etc
The 2014 and 2015 press kits have a pretty good summary of the changes here:
http://www.zeromotorcycles.com/press/