Will the Tascam handle a raw 13.5vdc from a SLA battery?
should be fine, even 6v slas arent at 6v, they should be at about 7-7.5v fully charged
the same goes for 12v slas, theyre fully charged float around 13.5-14 v
so yes that should be fine
if your batts hit exactly 6v or 12v, guess what, they just died on you