14 Cell Chargers
 

The Hyperion chargers can charge 14 nimh/nicad cells, so could I get a y-harness and charger 2 batteries at once?

Short answer: yes, as long as the total cell count does not exceed 14 cells.

Long answer: Be sure to look at the power limit. A lot of chargers can charge higher cell counts, or high currents, but not both at once. For example, if you have 2 X 7 cell packs (14 cells total) rated for 3800mAh, and you have a 50w limit charger, you'll only be able to charge at 2.97A (@1.2v/cell). Since NiMH peaks as high as ~1.4v/cell, the limit will be 2.55A. Even at the beginning of the charge where the cells are at ~1.1v/cell, you'll only be able to charge at 3.25A. As the cells charge and the voltage rises, the current will fall to maintain 50w output.