This is a circuit which uses a single Nickel-metal hydride battery to provide an output with discharge characteristics of a Lithium-ion battery. While waiting to fulfill a battery lead-time problem, the circuit can be used to complete a product.
A step-up converter provides the higher Voltage, and power control capability utilizes a burst mode circuit to limit shutdown power consumption.
For a full explanation and circuit diagrams, visit, http://www.elecdesign.com/Articles/Index.cfm?ArticleID=10082
Electronic Design, April 14, 2005