diff --git a/fittotcx.py b/fittotcx.py
index 69de2f4..468e6ca 100755
--- a/fittotcx.py
+++ b/fittotcx.py
@@ -24,8 +24,10 @@
 
 """Convert a FIT file to a TCX file"""
 
-import sys
 import lxml.etree
+import os
+import sys
+sys.path.append(os.path.dirname(__file__))
 import unitconvert
 
 from fitparse import Activity, FitParseError
@@ -113,18 +115,18 @@ def add_trackpoint(element, trackpoint):
     heart_rate = trackpoint.get_data("heart_rate")
     cadence    = trackpoint.get_data("cadence")
 
-    create_sub_element(element, "Time", timestamp.isoformat() + "Z")
+    create_sub_element(element, "Time", timestamp.isoformat())
 
     if pos_lat != None and pos_long != None:
         pos = create_sub_element(element, "Position")
-        create_sub_element(pos, "LatitudeDegrees", 
+        create_sub_element(pos, "LatitudeDegrees",
             str(unitconvert.semicircle_to_degrees(pos_lat)))
         create_sub_element(pos, "LongitudeDegrees",
             str(unitconvert.semicircle_to_degrees(pos_long)))
 
     if altitude != None:
         create_sub_element(element, "AltitudeMeters", str(altitude))
-    if distance != None:    
+    if distance != None:
         create_sub_element(element, "DistanceMeters", str(distance))
 
     if heart_rate != None:
@@ -138,7 +140,7 @@ def add_trackpoint(element, trackpoint):
     if speed != None:
         exelem  = create_sub_element(element, "Extensions")
         tpx = create_sub_element(exelem, "TPX")
-        tpx.set("xmlns", 
+        tpx.set("xmlns",
             "http://www.garmin.com/xmlschemas/ActivityExtension/v2")
         tpx.set("CadenceSensor", "Footpod")
         create_sub_element(tpx, "Speed", str(speed))
@@ -165,7 +167,7 @@ def add_lap(element, activity, lap):
     #extensions
 
     lapelem = create_sub_element(element, "Lap")
-    lapelem.set("StartTime", start_time.isoformat() + "Z")
+    lapelem.set("StartTime", start_time.isoformat())
 
 
     create_sub_element(lapelem, "TotalTimeSeconds", str(totaltime))
@@ -202,7 +204,7 @@ def add_activity(element, activity):
 
     actelem = create_sub_element(element, "Activity")
     actelem.set("Sport", sport)
-    create_sub_element(actelem, "Id", identity.isoformat() + "Z")
+    create_sub_element(actelem, "Id", identity.isoformat())
 
     for lap in activity.get_records_by_type('lap'):
         add_lap(actelem, activity, lap)
diff --git a/unitconvert.py b/unitconvert.py
index 0f0e19d..99d7292 100644
--- a/unitconvert.py
+++ b/unitconvert.py
@@ -19,17 +19,102 @@
 # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 # FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 # DEALINGS IN THE SOFTWARE.
-
 """Unit conversions"""
 
-from time import mktime
-from datetime import datetime
+import datetime
+ZERO = datetime.timedelta(0)
+
 
 def semicircle_to_degrees(semicircles):
     """Convert a number in semicricles to degrees"""
     return semicircles * (180.0 / 2.0 ** 31)
 
+
 def local_date_to_utc(date):
     """Local date to UTC"""
-    return datetime.utcfromtimestamp(mktime(date.timetuple()))
+    return date.replace(tzinfo=UTC)
+
+
+class UTC(datetime.tzinfo):
+    """UTC
+
+    Optimized UTC implementation. It unpickles using the single module global
+    instance defined beneath this class declaration.
+    """
+    zone = "UTC"
+
+    _utcoffset = ZERO
+    _dst = ZERO
+    _tzname = zone
+
+    def fromutc(self, dt):
+        if dt.tzinfo is None:
+            return self.localize(dt)
+        return super(utc.__class__, self).fromutc(dt)
+
+    def utcoffset(self, dt):
+        return ZERO
+
+    def tzname(self, dt):
+        return "UTC"
+
+    def dst(self, dt):
+        return ZERO
+
+    def __reduce__(self):
+        return _UTC, ()
+
+    def localize(self, dt, is_dst=False):
+        '''Convert naive time to local time'''
+        if dt.tzinfo is not None:
+            raise ValueError('Not naive datetime (tzinfo is already set)')
+        return dt.replace(tzinfo=self)
+
+    def normalize(self, dt, is_dst=False):
+        '''Correct the timezone information on the given datetime'''
+        if dt.tzinfo is self:
+            return dt
+        if dt.tzinfo is None:
+            raise ValueError('Naive time - no tzinfo set')
+        return dt.astimezone(self)
+
+    def __repr__(self):
+        return "<UTC>"
+
+    def __str__(self):
+        return "UTC"
+
+
+UTC = utc = UTC() # UTC is a singleton
+
+def _UTC():
+    """Factory function for utc unpickling.
+
+    Makes sure that unpickling a utc instance always returns the same
+    module global.
+
+    These examples belong in the UTC class above, but it is obscured; or in
+    the README.txt, but we are not depending on Python 2.4 so integrating
+    the README.txt examples with the unit tests is not trivial.
 
+    >>> import datetime, pickle
+    >>> dt = datetime.datetime(2005, 3, 1, 14, 13, 21, tzinfo=utc)
+    >>> naive = dt.replace(tzinfo=None)
+    >>> p = pickle.dumps(dt, 1)
+    >>> naive_p = pickle.dumps(naive, 1)
+    >>> len(p) - len(naive_p)
+    17
+    >>> new = pickle.loads(p)
+    >>> new == dt
+    True
+    >>> new is dt
+    False
+    >>> new.tzinfo is dt.tzinfo
+    True
+    >>> utc is UTC is timezone('UTC')
+    True
+    >>> utc is timezone('GMT')
+    False
+    """
+    return utc
+_UTC.__safe_for_unpickling__ = True