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When we got our EV1, we thought it would be interesting to see just how much range we were getting, and how much variation there was in this range. We normally do this for our other cars when we gas up (we watch for sudden drops in mileage to indicate trouble), but for the EV1 it took a little while for us to figure out what to record...

The EV1 range plot shows our range per full charge calculated two ways. The first uses the trip odometer reading and the percent of charge used (starting charge minus ending charge). The second uses the trip odometer reading plus the EV1's estimated remaining range.

Click on the graph to get a full-size view.

The first method should be more accurate since the charge readings taken off the wall charger can be read to 1% (we're assuming accuracy=precision in this). In addition, it does not rely on the projected range which depends on how we were driving just prior to the end of the trip. However, if we use the 115V charger, we can't get the state of charge reading accurately since this charger doesn't have a charge state display. We suggest to GM that the car's display be modified to show the charge percentage inside the car no matter which charger is connected.

It's interesting to note that the range we're getting has remained fairly constant over the time we've had the car (or at least since we began recording the data). However, a distinct dip is visible around the 15,000 mile point, which corresponds to the January-March 1998 time-frame during which we had a delayed and prolonged cold/rain spell.

Note also that when the battery failure occurred, it was a sudden occurrence (i.e. no long term trend indication).


  • Trips of less than 20 miles total have been omitted because of the larger uncertainty in readings.
  • These measurements are biased toward freeway driving since most weekday use is for commuting, and most weekend use is for very short trips which are not recorded.

Uncertainties & Variables

This plot is subject to a number of uncertainties and variables:
  • Driving conditions:
    • Traffic flow
    • Terrain (hills)
    • Car temperature (day vs. night, winter vs. summer)
    • Accessory usage (heating/cooling, lights, etc.)
    • Driving style
  • Data uncertainties:
    • Charger percentage accuracy
    • Range estimate behavior

In general, we are driving (with 2 people in the car) about a 55-mile round-trip commute with 5-10 miles of surface street driving. The freeway section of our trip is slow rush-hour congestion for only about 1/4 of the distance since carpool lanes and the late hour of our return trip avoids most of the LA gridlock. The freeway section is moderately hilly (SR91-I5-SR55), but with no major hills to climb. Thus far we have not found it necessary to use heating or air conditioning much (usually just the fan).

For the most part, we drive the EV1 very conservatively (to insure that we can make it home!). But this is subject to some variation too. If we demonstrate the car to someone, we might demonstrate its acceleration capability, or if we know the trip will be well within range, we might be less conservative about getting onto the freeway or using accessories.

Besides the uncertainty about the charge percentage accuracy, we've noticed that after a night of charging, the charger will indicate a full charge, but if you unplug the paddle and immediately put it back in, it will typically read 96% or 97% and start the charging cycle to top it off (10-15 minutes). So far, we have not been able to get a clear answer on whether or not the charge really is not quite topped off, or the charger is just assuming that since it has just been re-energized, it needs to run a bit to top off the batteries.

The range estimate is a less reliable measure because it uses the most recent past history to project how much farther you can go. So if the last 5 miles happened to be on surface streets because we ran an errand before going home, the remaining distance will be quite different from our normal run straight home which is about 1/4 mile from the freeway exit.

Copyright 1997-1999 by Dave & Jean Kodama Email: kodama@alumni.caltech.edu