The MB-D12 multi-battery power pack for the Nikon D800/800E allows for more shooting time and additional battery options.  It is supplied with MS-D12EN for EN-EL15 Rechargeable Li-ion Battery (sold separately) and MS-D12 for 8 AA batteries (not included).

Accepts 1.5V LR-6 (Alkaline), Lithium (FR6), Ni-MH (HR6) or Ni-Mn (ZR6).