Theoretically, two Madmaxs in parallel should work. I've never tried it before so I'm not positive about the outcome.
A converter(s) wired up to drive 700mA regulated CC to a typical white LED assuming Vf of 3.5V would be boosting 1.2V to 3.5V or a ratio of 2.9:1. A 100% efficient converter(s) would then be drawing 2.9 * 700mA from a 1.2V battery or ~2A. As the battery voltage drops the battery current would go up as battery voltage drops. At 1V the battery current would rise to ~2.45A at 100% efficiency.
Most converters especially at the low voltage end are rarely over 80% efficient. With 80% efficiency the 1V current would be more like 3A.
The Madmax max input current is limited to 1A. Two of these would max be 2A.
You can make two Zetex drivers that combined will probably get you the 700mA you desire. Each Zetex driver would be configured for 350mA @ 1.2V and they would be semi-regulated and @1V would deliver something slightly less than 350mA.
Getting an extremly low Vf is critical to keeping the demand on the battery minimized. There is a big difference between a 3.5Vf and a 3.0Vf LED in this type of application.
-Wayne
