I'm gonna guess that you were running those 2 4S packs in parallel for 14.8v.
The components inside the Mamba Monster will instantly fry if you put 29.6v through them. Trust me, it was a very big deal to step up the FET's beyond 25v hardware. I can link you the fet number if you really want to do the research into what it will handle.
Maybe you are talking about NIMH batteries and not Lithium polymer?