Mixed-mode is used to describe a trip in which multiple modes of operation were used, including charge-depleting, blended, and charge-systaining modes.
Blended mode is a mode of operation of a Plug-in hybrid electric vehicle in which a portion of the motive energy is supplied by the electric portion of the system who's batteries are recharged from an external source. To contrast battery electric vehicles use only electricity as their fuel source, while existing hybrid electric vehicles use only gasoline for fuel. Both types use regenerative brakeing to recapture kinetic energy, this should not be considered a fuel source but rather an efficiency aspect of these types of electric vehicle powertrains not found in traditional ICE vehicles without regen. Blended mode uses both gas and electricity as fuels and as such reduces the amount of gas used while displacing it with electricity. In such a mode of operation the gas mileage might be measured as double or more the mileage had only gas been used, but one should not forget to consider the amount of electricity which was used, normally measured in kWh. Since the electric energy stored onboard is substantially less than that of a tank of gas, typically less than 1/4 gallon equivalent, the blended mode range might also be reported as the distance that the available battery capacity can sustain such a mode. Of course driving conditions and speeds would effect the mileage and range just as it does a traditional ICE vehicles gas mileage. Such vehicles would also have unlimited range so long as a supply of gas were available and be able to operate as a gas only vehicle with normal mileage if not recharged, which wouldn't be required. Most vehicles would also have some amount of pure electric only range, and BEV's using pusher trailers or genset trailers can conversely give those vehicles unlimited range on gas as well as blended mode range.
Some early non-production Plug-in hybrid electric vehicle conversions have been based on the version of Hybrid Synergy Drive (HSD) found in the 2004 and newer model year Toyota Prius. Early PbA conversions by CalCars have demonstrated 10 miles of ev-only and 20 miles of double mileage blended mode range. A company planning to offer conversions to consumers named EDrive systems will be using Valence Li-ion batteries and have 35 miles of electric range. Both of these systems leave the existing HSD system mostly unchanged and would be similarly simply to apply to other hybrid powertrain flavors. Simply replacing the stock NiMH with a higher capacity battery pack and of course a charger to refill them for about $0.03 per mile from standard household outlets.
Though the Honda Integrated Motor Assist (IMA) systems does not have low speed electric only abilities blended mode mileage could be greatly enhanced while displacing some of their gas consumption with electricity from external sources. See the Manual Integrated Motor Assist article for more details about successful implementation of just such a conversion.
GM & Chrysler AHS2
The Advanced Hybrid System 2 (AHS2) could be offered with additional battery capacity and charging capabilities as an option, costing about $3000 if offered by the manufacturer. Though there are no plans to do so, this could prove an opportunity for General Motors and DaimlerChrysler's to overtake others who presently dominate the hybrid market by delivering a markedly more versatile and fuel efficient Hybrid.