I've seen several references to the "breaking in" phase of the first 2,000 to 3,000 miles. What exactly is being broken in? Is it the driver changing habits, the mechanical system, the electric system, the software, or some combination of these? I've only driven 1,800 miles or so and am looking forward to seeing some level of improvement.

 

Theres some speculation involved in any discussion of what is actually breaking in. Its probably a combination of the driver getting better at driving a "hybrid style", the bearings loosening a little, the piston rings seating better in the cylinder walls, valves etc..., and maybe even the battery going through a few cycles.

All engines even non-hybrids have a break in period. Thats why they usually suggest not driving a new vehicle on a freeway at one speed for long periods of time in the manuals during its "break in period". They suggest that for the first 3000 miles you should try to drive at various speeds. Or at least they used to.

If you look at the manuals for many of your rechargeable devices you often see them mention that the battery lifetime will improve after a few cycles....