A start-stop system using two different battery chemistries is now in the prototype phase, Johnson Controls officials said at the 2015 North American International Auto Show in Detroit.

Most conventional start-stop systems use a single lead-acid battery, typically a 12-volt absorbent glass mat (AGM) battery or an enhanced flooded battery (EFB). Johnson Controls says that its dual-battery design can provide a bigger performance payback for micro-hybrid electric vehicles.

The innovation with the two battery system is the combination of start-stop performance from an existing technology and an increase in charging performance from a lithium-titanate battery, according to Craig Rigby, advanced market technology strategist for Johnson Controls Power Solutions. He was quoted by Automotive Engineering magazine.

The company claims the design could lead to an additional fuel efficiency gain of 3-5% when compared to existing start-stop systems. Johnson Controls and Toshiba are collaborating on the lithium-titanate cell design.

The lithium-titanate battery will be in a hard case and have a prismatic shape. Overall package size for the configuration is approximately 7.4 in. (190 mm) high, 9.4 in. (240 mm) long, and 3.5 in. (90 mm) wide. Production is expected to start in 2018.

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