Leica GEB171 PN:727367 external battery. 
Rechargeable external Ni-Mh battery for TPS 400, 700, 800, 1100, 1200, GPS500, GPS1200, DNA digital levels. The battery gives you over a days use from one charge and clips on to the side of any normal tripod. 
12 volt, 10 Ah.
 
Battery + Charge Kit Option Includes:
Leica GEB171 external battery
External battery to GPS  cable, PN:GEV97
Battery charger, PN:GGKL22