You ask which technique is better for the environment. Just let the car decide when to charge the battery, and drive as calmly as possible, as little as possible, if you want to do your part for the environment. Your battery gauge will rarely read 100%, but that is ok. The point isn't to have a charged battery, the point is to use less gas going to work/shopping or whatever you do.To understand the hybrid system a little better, consider this: Never rev your engine or drive just to charge the battery, because there are losses in the battery system. It's better to take the power coming out of the engine and directly apply it to your motion than to reroute it to a dynamo, charge your batteries, get it back via an electric motor. The batteries and the dynamo/motor are there just to get some power via regenerative braking that otherwise would have gone to heat the brakes, and to assist an engine that would otherwise be too small for the American driver's expectations.Finally, consider this extreme example:One driver drives her Civic Hybrid from San Francisco to Portland and back, getting 53 mpg. Another drives from San Francisco to Oakland and back, getting 41 mpg. Which person used less gas? The point, again, isn't about getting better mileage, or keeping your battery at 100%.