^^ The first time I ran my 60D it was under similar circumstances to you but not quite exact: was using a fully charged 3000 mAh external battery and had a set of newly charged Eneloop batteries (~1800-2000 mAh, I believe) in the deck. Running two channels with 48v phantom on at 24/48, the deck was powered up and recording for over 3 hours straight. By the end of that time the external battery was done, the deck automatically switched over to internal batteries and the meter was at two bars out of four. I wouldn't call that a definitive test, but I'm guessing you should be OK, dank.