A number of companies are investigating the possibility of adding an auxiliary power unit (APU) to the automobile to supply power when the engine is off. These APUs will have higher fuel-to-electric conversion efficiency because of the direct chemical-to-electrical conversion. Delphi and BMW have been developing a solid oxide fuel cell for use as an APU. The units have an output of 3-5 kW at 42 V. Although fuel cells are expensive, the use of an APU will allow a number of accessories to operate with the engine off and could supply power to an ISA for accelerating from the stop mode. DaimlerChrysler has been working on a fuel cell to power the air conditioner with the engine off to maintain a constant interior temperature.

General Motors has been working on a number of fuel cell vehicles and projects such as the HydroGen1. The Opel Zafira is a five seater van that is propelled by a 55 kW (75 hp) three phase electric motor that gives the vehicle a top speed of 140 km/h. It is powered by the HydroGen1 fuel cell.

General Motors and ExxonMobil Corp. have developed an efficient on-board fuel processor or reformer for a fuel cell that can extract up to 80% of the hydrogen in gasoline. According to GM, this could mean fuel cell powered vehicles could be a reality in about 10 years.

Advancements are being made in the area of fuel cells, it is unclear whether they will be used as the sole power source to power an electric vehicle or be used as an APU in the ISA-equipped 42 V vehicles. This opens the door to another set of scenarios as some people are referring to an ISA-equipped vehicle as a "light" hybrid.

Once the decisions on the generation, storage, and distribution have been made, the implementation of the 42 V system can progress further and full advantage of it can be realized. A number of technologies such as electric steering, electric brakes, fully-active suspension systems, and the electromechanical actuation of the engine valves are being developed and will be added as the infrastructure can support them. A number of other items such as electric oil pumps, electric air conditioning compressors, and electric water pumps are being developed.

It has been estimated that adoption of the 42 V electrical system and using it to its fullest could result in a 5-12% savings in fuel economy plus a lowering of exhaust emissions in the range of 10-15% depending on the configuration.